Etymologically
Log in

radius

This is the current revision of this entry, as edited by bogdan on 15 October 2026 at 19:30. This address is a permanent link to this version.
Changes in this edit History

Pronunciation

  • IPA (Classical): [ˈra.di.ʊs][1]
  • IPA (Ecclesiastical): [ˈraː.di.us][1]

Forms

radius m (genitive radiī or radī); second declension[1]

Etymology

The origin is uncertain.[2][1][3] Walde–Hofmann and Pokorny connected it with rādīx “root”, but de Vaan finds this unlikely because the meanings are so different, and sees no clear root for it.[2][1] The TLL derives it from a root *radh- “to shine”, comparing Old Norse röðull (“sun”).[4]

Earliest recorded meaning

It is found from Plautus onwards,[2][5] whose boastful soldier wants his shield to shine brighter “than the rays of the sun on a clear day”.[3]

Semantic evolution

It meant a ray of light, as in Ennius, and the spoke of a wheel, as in Virgil.[3] It was a staff or stake, and especially the pointed rod with which geometers drew figures in the sand, so that Cicero calls Archimedes a man “of the dust and the rod”.[3][6]

It also meant the radius of a circle, a weaver's shuttle, the spur on a bird's leg, the radius bone of the forearm, and a long kind of olive, as in Virgil.[1][3] Medieval writers used it in optics for a ray.[7] It survives as Italian raggio, French rai, Spanish rayo, Portuguese raio and Romanian rază.[1] English ray came through Old French in the early 14th century, and radius was taken from Latin in the 1590s.[8]

Timeline

  • c. 250–184 BC – Plautus uses it for the rays of the sun.[3][5]
  • 204–169 BC – Ennius uses it for rays of light.[3][5]
  • 81–43 BC – Cicero uses it for the geometer's rod.[3][5]
  • 70–19 BC – Virgil uses it for spokes and for a kind of olive.[3][5]
  • early 14th century – English ray is first recorded.[8]
  • 1590s – English radius is first recorded.[8]

Meanings

Noun

  1. A ray (of light).[3][9]
  2. A spoke (of a wheel).[3][1]
  3. A staff, rod; a stake.[9][6]
  4. A geometer's rod (for drawing).[3][6]
  5. The radius (of a circle).[1]
  6. A weaver's shuttle.[1]
  7. The radius bone (of the forearm).[1]
  8. A long variety of olive.[3][1]

Word family

  • radiātus
  • radiolus
  • radiōsus
  • radiō
  • English ray
  • English radius
  • English radiant
  • English radio

References

  1. ^ a b c d e f g h i j k l Wiktionary, the free dictionary, https://en.wiktionary.org
  2. ^ a b c de Vaan, Michiel (2008), Etymological Dictionary of Latin and the other Italic Languages, Leiden Indo-European Etymological Dictionary Series 7, Leiden; Boston: Brill
  3. ^ a b c d e f g h i j k l m Glare, P. G. W., ed. (2012), Oxford Latin Dictionary, 2nd ed., Oxford: Oxford University Press
  4. ^ Thesaurus linguae Latinae (1900–), Leipzig: Teubner; Berlin: De Gruyter; open-access ed., Munich: Bayerische Akademie der Wissenschaften
  5. ^ a b c d e Köbler, Gerhard (2010), Lateinisches Abkunfts- und Wirkungswörterbuch für Altertum und Mittelalter, online ed., koeblergerhard.de
  6. ^ a b c Gaffiot, Félix (2016), Dictionnaire latin-français, new ed. by Gérard Gréco et al. (Gaffiot 2016), online ed.
  7. ^ Latham, R. E., D. R. Howlett, R. K. Ashdowne, et al. (1975–2013), Dictionary of Medieval Latin from British Sources, London: British Academy / Oxford University Press
  8. ^ a b c Harper, Douglas. Online Etymology Dictionary, https://www.etymonline.com
  9. ^ a b Lewis, Charlton T.; Short, Charles (1879), A Latin Dictionary, Oxford: Clarendon Press