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Etymology 1Edit

From Proto-Indo-European *h₂eḱ- (sharp). Related to acuō (sharpen, whet) and aciēs (edge).


acus f (genitive acūs); fourth declension

  1. a needle, a pin
  2. bodkin

Fourth-declension noun.

Case Singular Plural
Nominative acus acūs
Genitive acūs acuum
Dative acuī acibus
Accusative acum acūs
Ablative acū acibus
Vocative acus acūs
Derived termsEdit
  • Neapolitan: aco
  • Romanian: ac
  • Sardinian: àcu
  • Vulgar Latin: *acūcla (see there for further descendants)

Etymology 2Edit

From Proto-Indo-European *h₂eḱ- (sharp), cognates including agna (ear) and Proto-Germanic *ahaz (ear), Proto-Germanic *aganō, *ahanō (chaff) (> English awn), Ancient Greek ἄχυρον (ákhuron), Greek άχυρο (áchyro, hay).


acus n (genitive aceris); third declension

  1. bran
    Synonym: āplūda

Third-declension noun (neuter, imparisyllabic non-i-stem).

Case Singular Plural
Nominative acus acera
Genitive aceris acerum
Dative acerī aceribus
Accusative acus acera
Ablative acere aceribus
Vocative acus acera
Derived termsEdit


  • Ernout, Alfred; Meillet, Antoine (2001), “acus”, in Dictionnaire étymologique de la langue latine: histoire des mots (in French), with additions and corrections of André J., 4th edition, Paris: Klincksieck, page 7
  • acus in Charlton T. Lewis and Charles Short (1879) A Latin Dictionary, Oxford: Clarendon Press
  • acus in Charlton T. Lewis (1891) An Elementary Latin Dictionary, New York: Harper & Brothers
  • acus in Charles du Fresne du Cange’s Glossarium Mediæ et Infimæ Latinitatis (augmented edition, 1883–1887)
  • acus in Gaffiot, Félix (1934) Dictionnaire Illustré Latin-Français, Hachette
  • Carl Meissner; Henry William Auden (1894) Latin Phrase-Book[1], London: Macmillan and Co.
    • you have hit the nail on the head: rem acu tetigisti
  • acus in Harry Thurston Peck, editor (1898) Harper's Dictionary of Classical Antiquities, New York: Harper & Brothers
  • acus in William Smith et al., editor (1890) A Dictionary of Greek and Roman Antiquities, London: William Wayte. G. E. Marindin