LATIN DICTIONARYLexicon Latīnum
noun · masculinesecond declension

radius

radius m (genitive radiī or radī)
Classical[ˈra.di.ʊs]Ecclesiastical[ˈraː.di.us]

Meaning

  1. masculinea spoke of a wheel
  2. masculinea rod for measurement
  3. masculinethe radius of a circle; a rotating radial arm
  4. masculinea shuttle
  5. masculinepoetica bolt or shaft
  6. masculinethe spur of a bird's leg
  7. masculinethe tail-spine of a stingray
  8. masculinethe radius (the outer bone of a forearm)
  9. masculinea ray of light (also reflected)
    “[...] ubi prīmōs crāstinus ortus“… when at tomorrow’s early dawn the Titan [Sun] will have risen, and with [his] rays revealed the world.”29 BCE – 19 BCE, Vergilius, Aeneis 4.118-119
    At pater Hēliadum radiōs ubi tīnxerit undīsBut when the father of the Heliades shall have dipped his rays in the waves …. (The father is the sun god; see: Heliades.)8 CE, Ovidius, Fasti 6.717
  10. masculinea ray extending from the eye to the object seen
  11. masculinethe name of an elongated variety of olive
  12. masculinethe name of a rod with which geometers make figures in dust, also known as a virga

Latīnē defined in Latin in our graded readers

virga rotae; etiam līnea lūcis
radius -ī (m) — in Metamorphoses I, ch. 5, 12

Declension

declension
formsingularplural
nominativeradiusradiī
genitiveradiī
radī		radiōrum
dativeradiōradiīs
accusativeradiumradiōs
ablativeradiōradiīs
vocativeradieradiī

rădĭus, ii, m. cf.: radix, ramus,
I. a staff, rod.
I. In gen.: acuti radii immissi, stakes, Liv. 33, 5, 11: ferreus, Plin. 10, 42, 58, § 117.—
B. In partic.
1. A spoke of a wheel, Plin. 16, 40, 76, § 206; Verg. G. 2, 444; id. A. 6, 616; Ov. M. 2, 108; 2, 317; Val. Fl. 6, 414: inter radios rotarum, Curt. 4, 9, 5; Plin. 16, 40, 76, § 206.—
2. In mathematics,
a. A staff, rod, for measuring, etc., Cic. Tusc. 5, 23, 64; Verg. E. 3, 41; id. A. 6, 850; Macr. S. 7, 2; Tert. Idol. 9. —
b. A semidiameter, radius of a circle, Cic. Univ. 6. —
3. In weaving, a shuttle, Ov. M. 6, 56; 132; Lucr. 5, 1352; Verg. A. 9, 476.—
4. In zoology,
a. The spur of many kinds of birds, Plin. 11, 47, 107, § 257; esp. of the cock, id. 30, 11, 29, § 97. —
b. The sting above the tail of the fish pastinaca, Plin. 9, 48, 72, § 155; 32, 2, 12, § 25. —
5. In botany, a kind of long olive, Verg. G. 2, 86; Col. 5, 8, 4; id. Arb. 17, 3; Plin. 15, 3, 4, § 13. A sub-species of the same, called radius major, Cato, R. R. 6, 1; Varr. R. R. 1, 24.—
6. In anatomy, the radius, the exterior bone of the forearm, Gr. κερκίς, Cels. 8, 1. —
7. Radius virilis = membrum virile, Cael. Aur. Acut. 3, 14, 115.—
II. A beam or ray of any shining object; of the sun, Plaut. Mil. 1, 1, 2; Lucr. 1, 48; 2, 117; Cic. Fin. 5, 24, 71; Verg. A. 4, 119; 7, 25; Tert. Res. Carn. 47; of lightning, Verg. A. 8, 429; Val. Fl. 6, 55; of the eyes, Gell. 5, 16, 2; of the halo around the heads of divine or deified personages: aurati, Verg. A. 12, 163; cf. radio, II.

Origins

Of uncertain origin. Some connect it with rādīx and rāmus. Tucker suggests Proto-Indo-European *neredʰ- (“extend forth, rise, outward”) akin to Sanskrit वर्धते (vardhate, “rise, grow”), or from Ancient Greek ἄρδις (árdis, “sharp point”). May ultimately be from Proto-Indo-European *reh₁t- (“bar, beam, stem”).

Descendants
  • Catalanraig
  • Sardinianraxufrom Catalan raig
  • Frenchraifrom Old French rai
  • Englishrayfrom Old French rai
  • Italianraggio
  • Italianrazzo
  • Occitanrai
  • Portugueseraia
  • Portugueseraio
  • Romanianrază

In English words that came into English from radius

  • rayradius
  • radiusradius
  • radiantradiāns
  • radiationradiatio
  • radiateradiātus
  • radialradiālis
  • rayonradius
  • radioleradiolus
  • irradiateirradiātus

In the Academy Smith's classical dictionaries

AntiquitiesRadiusRadius 1. A straight pointed rod used by geometricians and astronomers for describing figures on their abacus, a table covered with sand. (Cic. Tusc. …

Quick answers

What does radius mean in Latin?
radius, a noun, means “a ray of light (also reflected); the name of an elongated variety of olive; the name of a rod with which geometers make figures in dust, also known as a virga”.
What is the genitive of radius?
The genitive singular is radiī. radius is masculine, second declension.
How do you pronounce radius?
In classical Latin, [ˈra.di.ʊs]; in ecclesiastical (church) Latin, [ˈraː.di.us].
Which English words come from radius?
English words that go back to Latin radius include ray, radius, rayon, radiant, radiate and radial.