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mendax

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Etymology and origin of the Latin word mendax

Confidence
Probable
Formation
Derivation
First attested
c. 250–184 BC, Plautus
Ultimate origin
Latin (mendum)

Pronunciation

  • Classical: [ˈmɛn.daːks][1]
  • Ecclesiastical: [ˈmɛn.daks][1]

Forms

mendāx (genitive mendācis, comparative mendācior, superlative mendācissimus, adverb mendāciter); third-declension one-termination adjective[1] Plautus has an ablative singular mendāce.[2]

Etymology

The OLD forms it from mendum (“fault, blemish”) with the suffix -āx;[2][3] Wiktionary takes the first sense to have been “faulty”, turned to “deceitful” under the influence of mentior (“to lie”),[1] from which Lewis and Short derive it directly.[4] Köbler gives both explanations.[5] De Vaan reconstructs ⟨mendum⟩ as Proto-Italic *m(e)ndo-, cognate with Old Irish mennar (“blemish”), but calls any further derivation merely theoretical.[3]

Earliest recorded meaning

De Vaan dates it from Plautus,[3] where someone is told “let them call you a liar, untruthful, with no good faith”.[2]

Semantic evolution

It is prone to tell falsehoods, untruthful, and lying on a given occasion, as Plautus' “so that he may not lie to me”;[2][4] Cicero notes that we do not believe a liar even when he tells the truth.[2][4] Of reports and dreams it is false, as Cicero's minds stirred by false and lying visions, and of things it is deceptive, as Horace's farm that fails its owner's hopes.[2] It is also that which falsely pretends to be something, as Catullus' false pregnancy.[2] As a noun it is a liar.[1][4]

Church Latin glosses it “false, deceitful, unreliable, prone to lying”.[6] English mendacious is from its derivative mendācium “lie” in the 1610s.[7]

Timeline

  • c. 250–184 BC – Plautus of a liar.[2][5]
  • 81–43 BC – Cicero of lying visions.[2][5]
  • 81/79–52/50 BC – Catullus of a false pregnancy.[2][5]
  • 65–8 BC – Horace of a deceptive farm.[2][5]

Meanings

Adjective

  1. Given to lying, untruthful, mendacious.[2][4][1][6]
  2. Of reports or dreams, false.[2]
  3. Deceptive, giving a false impression.[2]
  4. Falsely pretending to be.[2]

Noun

  1. A liar.[1][4][6]

Word family

References

  1. ^ a b c d e f g Wiktionary, the free dictionary, https://en.wiktionary.org
  2. ^ a b c d e f g h i j k l m n o Glare, P. G. W., ed. (2012), Oxford Latin Dictionary, 2nd ed., Oxford: Oxford University Press
  3. ^ a b c de Vaan, Michiel (2008), Etymological Dictionary of Latin and the other Italic Languages, Leiden Indo-European Etymological Dictionary Series 7, Leiden; Boston: Brill
  4. ^ a b c d e f Lewis, Charlton T.; Short, Charles (1879), A Latin Dictionary, Oxford: Clarendon Press
  5. ^ a b c d e Köbler, Gerhard (2010), Lateinisches Abkunfts- und Wirkungswörterbuch für Altertum und Mittelalter, online ed., koeblergerhard.de
  6. ^ a b c Stelten, Leo F. (1995), Dictionary of Ecclesiastical Latin, Peabody, Mass.: Hendrickson
  7. ^ Harper, Douglas. Online Etymology Dictionary, https://www.etymonline.com
Cite this entry

“Mendax.” Etymologically, 19 Oct. 2026, etymologically.com/la/mendax. Accessed 19 Oct. 2026.

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