acus

• (Classical) IPA^(key): /ˈa.kus/, [ˈa.kʊs]

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.

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).

• acerātus
• acerōsus

• 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, 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