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radius

Etymology and origin of the English word radius

History Permalink
Confidence
Established
Formation
Borrowing
First attested
1578
Borrowed from
Latin radius
Ultimate origin
Latin (radius)
Etymology tree
inherited borrowed derived
Latin radius
English radius

Pronunciation

  • IPA: /ˈɹeɪ.di.əs/[1]

Etymology

It is borrowed from Latin radius (“staff, rod; spoke of a wheel; ray of light”),[2][3][4] a word of unknown origin,[3] perhaps related to rādīx (“root”), though de Vaan finds that unlikely.[3] It is a doublet of ray.[2]

Earliest recorded meaning

The staff of a cross-staff, a straight rod: 1597 in Barnhart and the OED, the 1590s in Etymonline;[2][5][3] Merriam-Webster dates a sense to 1578.[6]

Semantic evolution

As the shorter bone of the forearm it is from 1615 (the 1610s), as in Latin.[5][3][4] The geometric sense, a line from the centre of a circle to the circumference, is first recorded in Hobbes's Six Lessons (1656),[2][3] and a circular area of a given distance around a place from 1853.[3] The classical plural is radii.[3][7] The verb, to round off a corner, is from 1938.[5]

Timeline

  • 1578 – radius (Merriam-Webster).[6]
  • 1597 – the staff of a cross-staff.[2][5]
  • 1615 – the forearm bone.[5]
  • 1656 – the radius of a circle.[2]
  • 1853 – a circular area.[3]

Modern meaning

Noun

  1. A straight line from the centre of a circle or sphere to its edge, or its length.
  2. A circular area within a given distance of a place: within a ten-mile radius.
  3. (anatomy) The shorter, thicker of the two bones of the forearm.

Word family

  • circumradius
  • inradius
  • triradius
  • Bohr radius
  • hydraulic radius
  • radius of convergence
  • radius of curvature

References

  1. ^ Wiktionary, the free dictionary, https://en.wiktionary.org
  2. ^ a b c d e f Barnhart, Robert K. (1988), The Barnhart Dictionary of Etymology
  3. ^ a b c d e f g h i Harper, Douglas. Online Etymology Dictionary, https://www.etymonline.com
  4. ^ a b Hoad, T. F., ed. (1986), The Concise Oxford Dictionary of English Etymology, Oxford: Clarendon Press
  5. ^ a b c d e Simpson, J. A.; Weiner, E. S. C., eds. (1989), The Oxford English Dictionary, 2nd ed., Oxford: Clarendon Press
  6. ^ a b Merriam-Webster Unabridged Dictionary (2024), online ed., Springfield, Mass.: Merriam-Webster
  7. ^ Collins English Dictionary (2023), Glasgow: HarperCollins

Related etymologies

Cite this entry

“Radius.” Etymologically, 17 Oct. 2026, etymologically.com/en/radius. Accessed 17 Oct. 2026.

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