perfidious

C1 Topic:Describing Qualities

US /pɚˈfɪdiəs/ UK /pəˈfɪdiəs/ See IPA manual

adj

Meanings

1

adj
deceitful and untrustworthy

He was a perfidious ally, betraying us at the first opportunity.

Thesaurus

Synonyms

1 adj · deceitful and untrustworthy treacherous disloyal unfaithful duplicitous insidious

Opposites

loyal faithful trustworthy honest

Etymology

From Latin per- ('through') + fidere ('to trust'), forming perfidus ('faithless; treacherous'); via Old French perfide into Middle English perfidious 'deceitful; treacherous'.

Topics

Describing Qualities Word Formation & Derivatives

# perfidious

**Type:** Word
**Level:** C1
**Part of speech:** adj
**IPA (US):** pɚˈfɪdiəs
**IPA (UK):** pəˈfɪdiəs

## Meanings
1. deceitful and untrustworthy

## Examples
- He was a perfidious ally, betraying us at the first opportunity.

## Synonyms
- treacherous
- disloyal
- unfaithful
- duplicitous
- insidious

## Antonyms
- loyal
- faithful
- trustworthy
- honest

## Etymology
From Latin per- ('through') + fidere ('to trust'), forming perfidus ('faithless; treacherous'); via Old French perfide into Middle English perfidious 'deceitful; treacherous'.

## AI Etymology
Perfidious comes from Latin per- ('through') + fidere ('to trust'), forming perfidus ('faithless; treacherous'); via Old French perfide into Middle English perfidious 'deceitful; treacherous'. In current use it is an adjective meaning "deceitful and untrustworthy". That sense is explained by the older material without requiring a speculative semantic step: the inherited or borrowed base supplies the field of meaning, while the English formation fixes its modern role. The surface form is compositional: its joined elements remain visible in the modern word. The word's history is thus visible in its construction: the components remain interpretable even after the whole expression has settled into a conventional English meaning.

## Topics
- Describing Qualities
- Word Formation & Derivatives

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