perfidy

UK: /ˈpɜː^rfədi/ US: /ˈpɝfɪdi/ ,(pûr′fi dē)

Inflections of 'perfidy' (n): npl: perfidies

WordReference Random House Learner's Dictionary of American English © 2026

per•fi•dy /ˈpɜrfɪdi/   n., pl. -dies. 

1. deliberate treachery or betrayal of another:
   [uncountable] Perfidy should not go unpunished.
2. [countable] an act or instance of being perfidious.

See -fid-.

WordReference Random House Unabridged Dictionary of American English © 2026

per•fi•dy  (pûr′fi dē), n., pl. -dies. 

1. deliberate breach of faith or trust;
   faithlessness;
   treachery:
   perfidy that goes unpunished.
2. an act or instance of faithlessness or treachery.

• Latin perfidia faithlessness, equivalent. to perfid(us) faithless, literally, through (i.e., beyond the limits of ) faith (per- per- + fid(ēs) faith + -us adjective, adjectival suffix) + -ia -y³
• 1585–95

Synonyms

See disloyalty. 

Collins Concise English Dictionary © HarperCollins Publishers::

perfidy / ˈpɜːfɪdɪ/ noun ( -dies)

1. a perfidious act

Etymology: 16th Century: from Latin perfidia, from perfidus faithless, from per beyond + fidēs faith