mendacity (English)

Where does "mendacity" come from?

The English noun 'mendacity' traces back to Late Latin 'mendacitas'[1]. This Late Latin form combines the Latin adjective 'mendāx' meaning 'deceitful, deceptive, lying' with the suffix '-itās', which forms nouns indicating a state of being[1]. The Latin adjective 'mendāx' itself derives from the Proto-Indo-European root '*mend-', meaning 'to fault', with its original meaning of 'faulty' shifting toward 'deceitful' under the influence of the Latin verb 'mentior' meaning 'to deceive, lie'[1][2]. Alternatively, 'mendāx' may connect to 'mentior', which stems from 'mēns' or 'mentis' meaning 'mind' or 'thought', ultimately tracing back to the Proto-Indo-European root '*men-' meaning 'to think'[1][3][4][5].

Open questions

The derivation of mendāx is uncertain, as it may stem either from the Proto-Indo-European root *mend meaning to fault or from mentior meaning to deceive. [1]
The original meaning of mendax as faulty is understood to have shifted toward deceitful under the influence of mentior. [2]

Full etymology tree

mendacity (English), 'The fact or condition of being untruthful; dishonesty.'
- derived mendacitas (Late Latin)
  - derived mendax (Latin), 'deceitful, lying, deceptive, untruthful, false, mendacious, feigned, not real.'
    - derived *mend- (Proto-Indo-European), 'foal, small horse'
    - influence mentior (Latin), 'to lie, cheat, deceive'
      - derived mens (Latin), 'mind'
        inherited *mentis (Proto-Italic), 'mind, thought'
        inherited *méntis (Proto-Indo-European), 'thought'
        derived *men- (Proto-Indo-European), 'to think, mind'
        suffix *-tis (Proto-Indo-European), 'Derives abstract/action nouns from verb roots.'
  - suffix -itas (Latin), 'alternative form of -tās'

Ancestors

*men- (Proto-Indo-European)
mendax (Latin)
*méntis (Proto-Indo-European)
*mend- (Proto-Indo-European)

Sources

Updated August 2026

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Etymology data from Wiktionary, CC BY-SA 4.0 · About Miraris