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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.

Case Singular Plural
nominative acus acūs
genitive acūs acuum
dative acuī acibus
accusative acum acūs
ablative acū acibus
vocative acus acūs

Derived terms[edit]


  • Italian: ago
  • Romanian: ac
  • Sardinian: àcu
  • Vulgar Latin: *acūcla (see there for further descendants)


  • 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