Dictionary.com
Thesaurus.com
Synonyms

perfidious

American  
[per-fid-ee-uhs] / pərˈfɪd i əs /

adjective

  1. deliberately faithless; treacherous; deceitful.

    a perfidious lover.

    Synonyms:
    traitorous, unfaithful, disloyal, false
    Antonyms:
    faithful

perfidious British  
/ pəˈfɪdɪəs /

adjective

  1. guilty, treacherous, or faithless; deceitful

"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Other Word Forms

Etymology

Origin of perfidious

First recorded in 1530–40; from Latin perfidiōsus “faithless, dishonest”; cf. perfidy, -ous

Explanation

If someone accuses you of being perfidious, you should probably be offended — it means underhanded, treacherous, deceitful — even evil. If you betray people often, you're perfidious: traitors are extremely perfidious. Besides betrayal, this word implies lying and maybe other kinds of awful behavior, like stealing and taking bribes. Everyone tries to avoid perfidious people. Perfidious is kind of an old-fashioned word, but being perfidious will never go out of style, unfortunately.

Keep Reading on Vocabulary.com

Vocabulary lists containing perfidious

Example Sentences

Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.

Malodorous, Nefarious, Obstreperous, Perfidious -- I could go on all day.

From Washington Post • Aug. 2, 2018

Henry Metayer, author of a tragedy called the Perfidious Brother, committed it to Theobald, of Dunciad memory, for examination and correction.

From The Mirror of Taste, and Dramatic Censor, Vol. I, No. 6, June 1810 by Carpenter, S. C. (Stephen Cullen)

The "Perfidious Albion" of the opening of the century is the ally of France under Napoleon's heir; Russia, twice invaded by France, which looked on with satisfaction at French reverses, becomes its friend.

From The Crowd; study of the popular mind by Le Bon, Gustave

Perfidious Maid, I might have thought thou'dst prove False to thy Prince, and Rival in my Love.

From The Works of Aphra Behn, Volume III by Summers, Montague

"Perfidious wretch, you're capable of having talent—which of course will spoil everything!"

From The Tragic Muse by James, Henry