Words / O
English words starting with O
243 words, from Oak to Oxymoron. Levels A1 to C2. Each one opens a full lesson.
Oaknoun · A large tree with hard wood; also the wood itself.B1Oatcakenoun · A thin, dry biscuit made of oats, often eaten with cheese (especially Scottish).B1Oathnoun · A solemn promise, often legal or formal, to tell the truth or keep a duty.C1Obdurateadjective · Refusing to change your mind, even when people try to persuade you (formal).C2Obedientadjective · Willing to do what a person, rule, or order tells you.B2Obeseadjective · Very overweight in a medical sense (often with stated BMI criteria).B2Obeyverb · To do what a person, a sign, or a rule tells you to do.A2Obfuscateverb · To make something unclear on purpose, often with complicated language (formal).C2Objectnoun · A thing you can see or touch, but not a person or animal.A2Objectionnoun · A reason for being against a plan, idea, or decision.B1Objectivenoun · Something you are trying to achieve.B2Objectivitynoun · The quality of judging facts without personal feelings or bias.C1Objurgateverb · To rebuke someone harshly (formal / literary).C2Obligationnoun · Something you must do because of a law, contract, or duty (an obligation to / under).B2Obligatoryadjective · Required by a rule or law; you have no choice.B2Obligeverb · To force someone to do something by a rule or duty; be obliged to.B1Obliqueadjective · Not straight; also not said directly (an oblique reference).B2Obliterateverb · To destroy something completely, so that nothing remains (from destroy, already in the dictionary).C1Obliviousadjective · Not noticing what is happening around you (oblivious to / of).C1Obloquynoun · Strong public criticism, or the disgrace that follows it (formal).C2Obscureadjective · Not well known, or not easy to understand; also, hidden from view.C1Obsequiousadjective · Too eager to please someone in a position of power.C2Observableadjective · Able to be seen or measured (observable behaviour; an observable change).B2Observancenoun · The practice of following a law, custom, or religious rite (often uncountable).B2Observationnoun · The act of watching carefully; also a remark based on what you have noticed.B2Observeverb · To watch carefully, or to notice something.B1Observernoun · A person who watches an event, often officially, without taking part.B2Obsessverb · To fill someone’s mind so they cannot stop thinking about it (obsess about / over).B1Obsessionnoun · An idea or activity that you cannot stop thinking about, often too much.C1Obsessiveadjective · Thinking or doing something too much, in a way that is hard to stop.B2Obsoleteadjective · No longer used because something newer has replaced it.C1Obstaclenoun · Something that makes it difficult to achieve or continue something.B2Obstreperousadjective · Noisy, unruly, and difficult to control (formal).C2Obstructverb · To block a path, view, or process, or to prevent progress on purpose.C1Obstructionnoun · Something that blocks a path, view, or process; also the act of blocking (obstruction of justice).B2Obtainverb · To get something, especially by effort.B2Obtuseadjective · Slow to understand or insensitive; also (of an angle) greater than 90°.C2Obviateverb · To remove a need or a problem, so that it never arises.C2Obviousadjective · Easy to see or understand.B1Obviouslyadverb · In a way that is easy to see or understand; used to say something is clear.B1Occasionnoun · A particular time when something happens, often a special event.B1Occasionaladjective · Happening sometimes, but not regularly or often.B1Occasionallyadverb · Sometimes, but not regularly or often.B1Occludeverb · To block or close up a passage, opening, or view (formal / technical).C2Occupancynoun · The fact of a building being used, or how full it is (occupancy rates; maximum occupancy).B2Occupationnoun · A job or profession; also the act of living in or taking control of a place.B2Occupationaladjective · Relating to a person’s job or profession.C1Occupyverb · To fill a space, time, or position; also to take control of a place.B2Occurverb · To happen.B1Occurrencenoun · Something that happens, especially something unexpected or unwelcome; also how often it happens.B2Oceannoun · A very large area of sea.A2Octobernoun · The tenth month of the year.A1Oddadjective · Strange or unusual; also a number such as 1, 3, or 5.A2Oddsnoun · The chance that something will happen, often as a ratio; also, disagreement (at odds).C1Odiousadjective · Extremely unpleasant; deserving hatred.C2Odiumnoun · Widespread hatred or disgust felt towards a person or action (from hate, already in the dictionary).C1Odournoun · A smell, often one people notice or complain about (British spelling).B2Ofpreposition · Belonging to, or part of, something: a cup of tea; the name of the street.A1Offadverb · Away from a place or a surface; not on.A1Off-Licencenoun · A shop that sells alcohol to take away (UK; US liquor store).B1Off-Peakadjective · Cheaper or quieter because it is not the busiest time.B1Offencenoun · A crime (UK spelling); also the feeling of being insulted (take offence).B2Offendverb · To make someone upset or angry by what you say or do.A2Offendernoun · A person who has committed a crime.B1Offensiveadjective · Rude and likely to upset people; also used in sport for attacking play.B1Offerverb · To say you will give something or do something for someone.A2Offhandadjective · Without checking; also (disapproving) casual to the point of rudeness.B2Officenoun · A room or building where people work at desks.A1Officernoun · A person with authority in the police, armed forces, or an organisation.B2Officialadjective · Done by a person or group in authority.B1Officiousadjective · Too eager to tell people what to do, in an annoying official way.C2Offlineadjective · Not connected to the internet; also done in person rather than online.B1Offsetverb · To counterbalance an effect with an opposite one.C1Offspringnoun · A person’s or animal’s child or children (formal or scientific; same form in the plural).C1Oftenadverb · Many times; frequently.A2Oilnoun · A thick liquid from plants or the ground, used in cooking or as fuel.A2Okayexclamation · Used to agree, or to say that something is all right.A1Oldadjective · Having lived or existed for a long time.A1Old-Fashionedadjective · No longer modern in style, ideas, or clothes.A2Oleaginousadjective · Oily; unpleasantly ingratiating and insincere (formal / disapproving).C2Olfactoryadjective · Relating to the sense of smell (technical / formal).C2Olivenoun · A small green or black fruit, often in salads or on pizza.A1Omelettenoun · Eggs mixed and cooked flat in a pan (British spelling).A1Ominousadjective · Suggesting that something bad is going to happen.C1Omissionnoun · Something left out, or the act of leaving it out.C1Omitverb · To leave out a person, fact, or piece of information, either by accident or on purpose.B2Omnipotentadjective · Having unlimited power; able to do anything (from powerful, already in the dictionary).C1Omniscientadjective · Knowing everything (formal / literary).C2Onpreposition · Touching a surface, or about a day or date.A1Onceadverb · One time; also, at a time in the past: I met her once. Once, we lived there.A1Onenumber · The number 1.A1One-Wayadjective · Allowing travel or flow in only one direction (a one-way street / system).B1Onerousadjective · Needing a lot of effort or money; burdensome.C2Ongoingadjective · Continuing; not yet finished.B2Onionnoun · A round vegetable with a strong smell and taste, often used in cooking.A2Onlineadjective · Connected to the internet.A2Onlyadverb · No more than this; not anyone or anything else.A1Onsetnoun · The beginning of something, especially something unpleasant.C1Ontopreposition · To a position on a surface: onto the table; onto the bus.A1Onwardsadverb · From a time or place continuing forward (from 2019 onwards).B2Opaqueadjective · Not transparent; also hard to understand or see through.C2Openverb · To move something so it is not shut.A1Openingnoun · A hole or gap; also a job vacancy or the start of an event.B1Openlyadverb · In a way that does not hide your feelings or opinions.A2Operanoun · A play in which the words are sung, with an orchestra.A2Operateverb · To control a machine, or to cut someone in a hospital to treat them.A2Operationnoun · A planned activity, or medical surgery in hospital.A2Operationaladjective · Working and ready to be used; also, relating to the day-to-day running of a system.C1Operativeadjective · Working or in force; as a noun, a worker or agent.B2Operatornoun · A person who controls a machine or answers phone calls for a company.A2Opineverb · To express an opinion (formal; from comment, already in the dictionary).C1Opinionnoun · What you think about something; a personal view.A2Opponentnoun · A person or group you compete against or disagree with.B2Opportunisticadjective · Exploiting chances as they arise, often with little regard for principle.C1Opportunitynoun · A chance to do something useful or wanted.B1Opposeverb · To disagree with a plan or idea and try to prevent it.B2Oppositeadjective · Completely different, or on the other side.A2Oppositionnoun · Strong disagreement; also the political parties not in government (the Opposition).B2Oppressverb · To treat a group cruelly or unfairly, especially by using power.B2Oppressionnoun · Cruel or unfair control of people over a long period.C1Opprobriumnoun · Public criticism and strong disapproval.C2Optverb · To choose one thing rather than another (opt for / opt to / opt out).C1Optimismnoun · A tendency to expect that good things will happen.C1Optimisticadjective · Believing that good things will happen, or that a situation will improve.B2Optimumadjective · Best or most favourable for a particular purpose.B2Optionnoun · Something you can choose.A2Optionaladjective · You can choose to do it or not; not required.B2Opulencenoun · Great wealth, luxury, or abundance (from wealth, already in the dictionary).C1Orconjunction · Used to show a choice.A1Oraladjective · Spoken, not written; also connected with the mouth.A2Orangenoun · A round fruit with a thick orange skin, or the colour of that fruit.A1Oratornoun · A person who is skilled at making public speeches (from speaker, already in the dictionary).C1Orbitnoun · The curved path of a planet, moon, or satellite; also a sphere of influence.B2Orchestranoun · A large group of people who play classical music together.A2Ordainverb · To make someone a priest or minister; also to order something officially (from order, already in the dictionary).C1Ordealnoun · A very difficult, painful, or exhausting experience.C1Orderverb · To ask for food or goods in a restaurant or shop, or to tell someone to do something.A2Ordinancenoun · An official rule or local law (not ordnance, which is military weapons).B2Ordinaryadjective · Normal; not special or unusual.A2Organnoun · A body part with a function; also a church keyboard instrument, or a newspaper as a mouthpiece.B2Organicadjective · Grown or made without artificial chemicals.A2Organisationnoun · A company, charity, or official group; also the way things are planned (UK spelling).B1Organiseverb · To plan and arrange something.B1Organisernoun · A person who plans an event or a trip (British spelling).A2Orientverb · To find your position, or to direct something towards a purpose.B2Orientationnoun · A brief introduction to a new place or job; also the direction something faces, or a person’s attitude.C1Originnoun · The place, time, or cause where something begins.A2Originaladjective · First; not a copy, or new and not copied from others.B1Originallyadverb · In the beginning; before later changes.A2Originateverb · To begin or first appear in a particular place; to create something.C1Orotundadjective · Full, imposing, and often pompously resonant, of a voice or style (formal).C2Orphannoun · A child whose parents have died; as a verb, to leave someone without parents.B2Orthodoxadjective · Following the usual, accepted ideas or methods of a group.C1Ossifyverb · To harden into bone; of a system or habit, to become rigid and unable to change.C2Ostensibleadjective · Stated as the reason or appearance, but perhaps not the real one (formal).C2Ostentationnoun · Pretentious display intended to impress others.C2Ostentatiousadjective · Designed to impress others by showing off wealth or skill.C2Ostraciseverb · To refuse to include or talk to a person or group (UK spelling; from exclude, already in the dictionary).C1Otheradjective · Different from the one already mentioned; the remaining one.A1Otherwiseadverb · If not; in a different way.B1Oughtverb · Used with to to say that something is the right or sensible thing to do.A2Ouncenoun · A small unit of weight, about 28 grams.A2Ourdeterminer · Belonging to us.A1Ourspronoun · Belonging to us: This house is ours.A1Ourselvespronoun · We, used for emphasis or when we do something to us.A1Outadverb · Away from the inside of a place.A1Out-Of-Dateadjective · No longer valid, current, or safe to use.B1Outbreaknoun · A sudden start of something unwelcome, such as disease, violence, or fire.B2Outburstnoun · A sudden expression of strong feeling, or a sudden start of something.B2Outcomenoun · The final result of a process or event.B1Outcrynoun · A strong public expression of anger or protest.B2Outdatedadjective · No longer useful or fashionable because something newer exists.B2Outdooradjective · Used or happening outside, not in a building.A2Outdoorsadverb · Outside a building; in the open air.A2Outeradjective · On the outside, or further from the centre.A2Outfitnoun · A set of clothes worn together.A2Outingnoun · A short trip for pleasure, often for a group.A2Outlandishadjective · Looking or sounding extremely strange or unusual (from strange, already in the dictionary).C1Outlawverb · To make something illegal; as a noun, a person living outside the law.B2Outletnoun · A shop that sells a firm’s goods, often cheaper; also a way of expressing a feeling.B1Outlinenoun · A short description of the main points, without detail.B1Outliveverb · To live longer than someone or something, or to survive past a use.B2Outlooknoun · What is likely to happen; also a person’s general attitude.B2Outmodedadjective · No longer fashionable or useful; replaced by something newer (from obsolete, already in the dictionary).C1Outnumberverb · To be greater in number than someone or something.B2Outpatientnoun · A person who gets hospital treatment without staying overnight.B2Outpostnoun · A small military, trading, or organisational base far from the centre.B2Outputnoun · The amount of something a person, machine, or industry produces.B2Outragenoun · A strong feeling of shock and anger, or an act that causes it.C1Outrightadjective · Complete and total; also open rather than gradual or hidden.C1Outsetnoun · The start of something (from / at the outset).C1Outsidepreposition · Not in a building; on the outer side.A1Outskirtsnoun · The parts of a town or city that are furthest from the centre.A2Outspokenadjective · Saying what you think clearly, even if it shocks or offends.C1Outstandingadjective · Excellent; also not yet paid or dealt with (outstanding debts).B2Outwardadjective · Going away from a place, not returning.A2Outweighverb · To be more important or beneficial than something else.C1Ovennoun · The box inside a cooker that heats food from all sides.A1Oven Glovenoun · A thick glove for holding hot dishes from an oven (UK).B1Overpreposition · Above or across something; more than.A1Overalladjective · Including everything; general.B2Overbearingadjective · Trying to dominate other people in an unpleasant, arrogant way (from arrogant, already in the dictionary).C1Overboardadverb · Over the side of a ship; go overboard means do something to excess.B2Overcastadjective · Covered with cloud; dull and grey (an overcast sky).B2Overcoatnoun · A long warm coat worn over other clothes in cold weather.B2Overcomeverb · To succeed in dealing with a problem or fear.B2Overcrowdedadjective · Containing too many people or things for the space available.B2Overdraftnoun · Money a bank lets you spend when your account is empty, which you must repay.B2Overdueadjective · Not done or paid by the expected time.B2Overestimateverb · To guess a size, number, or ability as larger than it really is.B2Overflowverb · To spill over a limit, or (of a place) to be too full.B2Overhaulverb · To examine a system thoroughly and make major changes or repairs.C1Overhearverb · To hear what people are saying without them meaning you to listen.B2Overlapverb · To cover part of the same time, subject, or area as something else.B2Overloadverb · To put too much weight, work, or electric current onto something.B2Overlookverb · To fail to notice something; also to have a view over a place, or to choose not to punish a small fault.C1Overlyadverb · Too much; more than is reasonable.B2Overnightadverb · During the night; also suddenly, in a very short time.B1Overpowerverb · To defeat by greater strength, or to be too strong to bear.B2Overrideverb · To use authority to cancel a decision or an automatic setting.B2Overruleverb · To officially reject a decision by using higher authority.C1Overseasadverb · In or to a country across the sea; also an adjective (overseas students).B2Overseeverb · To watch work or a process to make sure it is done properly.B2Overshadowverb · To make a person or event seem less important; also to cast a shadow over.B2Oversightnoun · A mistake of not noticing something; also official supervision.C1Overstateverb · To describe something as greater, better, or worse than it really is.C1Overtadjective · Done or shown openly, not hidden.C1Overtakeverb · To go past a moving vehicle or person; also to catch up and become bigger.B2Overthrowverb · To remove a leader or government from power, especially by force.C1Overtimenoun · Extra hours you work after your usual time, or the pay for those hours.B1Overturnverb · To turn something upside down, or to reverse an official decision.B2Overviewnoun · A general description of a subject without going into detail.B1Overweeningadjective · Showing excessive pride or self-confidence (literary / formal).C2Overwhelmverb · To have such a strong effect that someone cannot cope; also to defeat completely.C1Overwroughtadjective · Extremely nervous or upset; of style, too elaborate.C2Oweverb · To need to pay money back, or to feel you should thank someone.A2Owingadjective · Still to be paid; owing to means because of.B2Owlnoun · A bird with large eyes that is usually active at night.A2Ownadjective · Belonging to you and not to anyone else.A1Ownernoun · The person that something belongs to.A2Ownershipnoun · The fact of owning something; also responsibility for a task (often uncountable).B1Oxygennoun · The gas in the air that people and animals need to breathe (uncountable).B1Oxymoronnoun · A phrase that joins two contradictory terms (rhetoric).C2