Words / C2

p-uh-FID-ee-uh-s/pəˈfɪdiəs/

Perfidious means cannot be trusted; willing to betray: a perfidious ally. Treacherous is a close synonym; disloyal is everyday and milder; two-faced overlaps with duplicitous. Perfidy is the noun. Literary/formal, historically loaded (perfidious Albion). In speech, treacherous or they sold us out is enough. A grave insult — not a word for a cancelled coffee.

Meaning

Cannot be trusted; willing to betray (literary/formal).

Examples

• “A perfidious ally leaked the plan.”
• “A perfidious leak from the steering group ended the confidential draft.”
• “Perfidious in the essay means betrayal, not a plot twist you disliked.”

Good to know

Treacherous; betraying (literary/formal). Noun: perfidy. Everyday: disloyal / treacherous. Serious charge. Close: duplicitous (two-faced dealing).

Near in meaning

treacherous

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