perfidious

adjective

per·​fid·​i·​ous (ˌ)pər-ˈfi-dē-əs 

: of, relating to, or characterized by perfidy

perfidiously adverb

perfidiousness noun

Did you know?

We wouldn't lie to you about the history of "perfidious" - even though the word itself suggests deceitfulness. The modern English meaning of "perfidious" remains faithful to that of its Latin ancestor, perfidus, which means "faithless." English speakers have used "perfidious" to mean "treacherous" since at least 1572. One of the earliest known uses of the term can be found in Act V, scene iii of Shakespeare’s All's Well That Ends Well: the "perfidious slave" Parolles is thought to be an unreliable witness; he’ll say whatever suits his purpose, whether true or not. In contemporary usage, "perfidious" not only implies treacherousness, but an inability to be reliable or honorable.

Synonyms

• disloyal
• faithless
• false
• fickle
• inconstant
• recreant
• traitorous
• treacherous
• unfaithful
• untrue

Choose the Right Synonym for perfidious

faithless, false, disloyal, traitorous, treacherous, perfidious mean untrue to what should command one's fidelity or allegiance.

faithless applies to any failure to keep a promise or pledge or any breach of allegiance or loyalty.

faithless allies

false stresses the fact of failing to be true in any manner ranging from fickleness to cold treachery.

betrayed by false friends

disloyal implies a lack of complete faithfulness to a friend, cause, leader, or country.

disloyal to their country

traitorous implies either actual treason or a serious betrayal of trust.

traitorous acts punishable by death

treacherous implies readiness to betray trust or confidence.

a treacherous adviser

perfidious adds to faithless the implication of an incapacity for fidelity or reliability.

a perfidious double-crosser

Examples of perfidious in a Sentence

We were betrayed by a perfidious ally.

a perfidious campaign worker revealed the senator's strategy to his leading rival for the nomination

Recent Examples on the Web

Since then, Putin has sought instead to rally the public to the defense of a motherland besieged by the perfidious and cunning West. —Leon Aron, The Atlantic, 5 Dec. 2024

And in this new era of Sino-Western rivalry, the Olympics are also used by more nationalistic elements of the Chinese media as a way to portray China in a positive light against the perfidious Americans and Europeans. —Alexander Smith, NBC News, 11 Aug. 2024

If Washington’s forays are conspicuous and its aims perfidious, its partners will not abet the next undertaking. —Mira Rapp-Hooper, Foreign Affairs, 3 Oct. 2019

In what might sound to many Americans like a familiar tactic, Netanyahu cast his critics and not himself as a threat to the country’s security, and sought to position himself as a victim of perfidious judges and prosecutors. —Tracy Wilkinson, Los Angeles Times, 27 Mar. 2023

Word History

First Known Use

1572, in the meaning defined above

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Kids Definition

perfidious

adjective

per·​fid·​i·​ous (ˌ)pər-ˈfid-ē-əs 

: of, relating to, or characterized by perfidy : treacherous

perfidiously adverb

perfidiousness noun