LATIN DICTIONARYLexicon Latīnum
noun · femininefourth declension

acus1

acus f (genitive acūs)
Classical[ˈa.kʊs]Ecclesiastical[ˈaː.kus]

Meaning

  1. femininea needle, a pin
  2. femininebodkin
  3. alternativefemininealternative form of acus (“bran”)
    nam sēmina excussa in āreā jacēbunt, superque eā paulātim eōdem modō reliquī fasciculī excutientur, ac dūrissimae quidem acūs rejectae sēparataeque erunt ā cūdentibus, minūtae vērō, quae dē siliquīs cum fabā resēderint, aliter sēcernentur.4 CE – c. 70 CE, Columella, De re rustica 2.14

Latīnē defined in Latin in our graded readers

ferrum tenue quō vestis pingitur
acus -ūs (f) — in Metamorphoses I, ch. 12

Declension

declension
formsingularplural
nominativeacusacūs
genitiveacūsacuum
dativeacuīacibus
acubus
accusativeacumacūs
ablativeacūacibus
acubus
vocativeacusacūs

Phrases from Meissner's Latin Phrase-Book

rem acu tetigisti
you have hit the nail on the head.

ăcus, ūs, f. cf. 2. acer.
I. A needle or pin, as being pointed, both for common use and ornament:quasarcinatrix veletiam ornatrix utitur, Paul. ex Fest. p. 9 Müll.
A. Lit.: mirabar vulnus, quod acu punctum videtur, Cic. Mil. 24.—Hence, acu pingere, to embroider, Verg. A. 9, 582; Ov. M. 6, 23; cf. Plin. 8, 48, § 191; Isid. Orig. 19, 22, 22.—Esp. a hair-pin: figat acus tortas sustineatque comas, Mart. 14, 24: foramen acūs, the eye of a needle, Vulg. Matt. 19, 24.—Also, a surgeon's needle, a probe, Cels. 7, 17.—Hence,
B. Trop.: acu rem tangere, to touch the thing with a needle; in Engl. phrase, to hit the nail on the head, Plaut. Rud. 5, 2, 19; so, to denote careful and successful effort: si acum quaereres, acum invenisses, id. Men. 2, 1, 13.—
II. The tongue of a buckle, Treb. Poll. Claud. 14.—
III. I. q. acus, ĕris, Col. 2, 10, 40.—
IV. An implement of husbandry, Pall. 1, 43, 2.
ăcus, i, m. 1. acus,
I. a kind of sea-fish with a pointed snout, the hornpike or gar-pike (Gr. βελόνη): acus sive belone unus piscium, etc., Plin. 9, 51, 76, § 166: et satius tenues ducere credis acos, Mart. 10, 37, 6; cf. Plin. 32, 11, 53, § 145, where belonae again occurs. (Some read una for unus in the passage from Plin., and acūs for acos in Mart., as if these forms belonged to 1. acus.)

Origins

The NIL suggests that the term was directly inherited from Proto-Indo-European *h₂eḱus (“pointed”), from the root *h₂eḱ- (“sharp”). However, De Vaan argues that the noun acus was a later formation from the same root. Though, De Vaan does suggest that this same Proto-Indo-European u-stem is the source of acūpedius and acuō (“to sharpen, whet”).

Italo-Dalmatian
  • Italianaco
  • Italianago
  • Corsicanacu
  • Dalmatianjuac
  • Istriotago
  • Neapolitanaco
Insular Romance
  • Sardinianàcu
Balkano-Romance
  • Romanianac
  • Aromanianac
  • Megleno-Romanianac
Gallo-Italic
  • Romagnolêg

In the Academy Smith's classical dictionaries

AntiquitiesAcusAcus, Greek (βελόνη, βελονίς, ῥαφίς, ἀκέστρα), a pin or needle, made sometimes of metal, sometimes of wood, bone, or ivory. They varied greatly in siz…
noun · neuterthird declension
acus2
acus n (genitive aceris)
Classical[ˈa.kʊs]Ecclesiastical[ˈaː.kus]

Meaning

  1. neuterbran, awn, chaff
    sī fēnum non erit, frondem īligneam et hederāceam datō. paleās trīticeās et hordeāceās, acus fabāginum, viciam, vel dē lupīnō, item dē cēterīs frūgibus omnia condito.234 BCE – 149 BCE, Marcus Porcius Cato, De agri cultura 54.2
    īs trītīs oportet ē terrā subjectārī vallīs aut ventilābrīs, cum ventus spīrat lēnis. ita fit ut quod levissimum est in eō atque appellātur acus ēvannātur forās extrā āream ac frūmentum, quod est ponderōsum, pūrum veniat ad corbem.116 BCE – 27 BCE, Marcus Terentius Varro, Rerum rusticarum 1.52

Declension

declension
formsingularplural
nominativeacusacera
genitiveacerisacerum
acuum
dativeacerī
acuī		aceribus
acibus, acubus
accusativeacus
acum		acera
ablativeacere
acū		aceribus
acibus, acubus
vocativeacusacera

ăcus, ĕris, n. (also, ūs, f., v. 1. acus, III.) [kindred with acus, ūs, Goth.
I. ahana, old Norse agn, old Germ. Agana], = ἄχυρον, the husk of grain and of pulse; chaff, Cato, R. R. 54, 2; Varr. R. R. 1, 52; 57; 3, 9, 8.

Origins

  1. Proto-Indo-European*h₂eḱ-
  2. Proto-Indo-European*h₂éḱos
  3. Proto-Italic*akos
  4. Latinacus

From Proto-Italic *akos, from Proto-Indo-European *h₂éḱos (“tip, bristle; ear/blade of grain, awn, chaff”), from the root *h₂eḱ- (“sharp”). Doublet of agna (“ear”). Cognates with Proto-Germanic *ahaz (“ear”), Proto-Germanic *ahanō (“chaff”), Ancient Greek ἄχυρον (ákhuron, “hay”), Tocharian B āke (“tip, peak, end”).

Italo-Romance
  • Neapolitanacere
Gallo-Romance
  • Old Occitanatx

In the Academy Smith's classical dictionaries

AntiquitiesAcusAcus, Greek (βελόνη, βελονίς, ῥαφίς, ἀκέστρα), a pin or needle, made sometimes of metal, sometimes of wood, bone, or ivory. They varied greatly in siz…

Quick answers

What does acus mean in Latin?
acus, a noun, means “a needle, a pin; bodkin; alternative form of acus (“bran”)”.
What is the genitive of acus?
The genitive singular is acūs. acus is feminine, fourth declension.
How do you pronounce acus?
In classical Latin, [ˈa.kʊs]; in ecclesiastical (church) Latin, [ˈaː.kus].