Etymologically
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diameter

Etymology and origin of the English word diameter

History Permalink
Confidence
Established
Formation
Borrowing
First attested
before 1387
Borrowed from
Old French diametre
Ultimate origin
Ancient Greek (διάμετρος)

Pronunciation

  • IPA: UK /daɪˈæm.ɪ.tə/, US /daɪˈæm.ə.t̬ɚ/[1]

Etymology

It is Middle English diametre, borrowed from Old French diametre,[2][3][4] from Latin diametrus, from Greek διάμετρος (diámetros, “diagonal of a circle or parallelogram”), short for diámetros grammḗ, the line measuring across,[2][3][5] from diá, across (see dia-), and μέτρον (métron, “measure”),[2][3] from PIE Proto-Indo-European *me- (“to measure”).[2]

Earliest recorded meaning

A straight line through the centre of a circle or sphere: before 1387, in Trevisa's translation of Higden's Polychronicon.[3][6]

Semantic evolution

A line passing through the centre of any body is from 1387,[6] and the transverse measurement or thickness of a figure from about 1391.[6] In arithmetic it meant the square root of the sum of the squares of two factors (1557),[6] and in architecture the width of a column at its base as a unit of measure (1604).[6] As a measure of the magnifying power of a lens, magnified 100 diameters, it is from 1856.[6] Diametrical is from 1553 and diametric from 1802.[3]

Timeline

  • before 1387 – a line through the centre.[3]
  • c. 1391 – the width of a figure.[6]
  • 1553 – diametrical.[3]
  • 1604 – in architecture.[6]
  • 1856 – of magnification.[6]

Modern meaning

Noun

  1. A straight line passing through the centre of a circle or sphere from one side to the other, or its length.
  2. The thickness or width of something round.

Word family

  • diametral
  • diametric
  • semidiameter
  • diametrical
  • diametrically
  • radius
  • meter

References

  1. ^ Jones, Daniel (2011), Cambridge English Pronouncing Dictionary, 18th ed., ed. Peter Roach, Jane Setter and John Esling, Cambridge: Cambridge University Press
  2. ^ a b c d Harper, Douglas. Online Etymology Dictionary, https://www.etymonline.com
  3. ^ a b c d e f g Barnhart, Robert K. (1988), The Barnhart Dictionary of Etymology
  4. ^ Merriam-Webster Unabridged Dictionary (2024), online ed., Springfield, Mass.: Merriam-Webster
  5. ^ Pearsall, Judy, ed. (1998), The New Oxford Dictionary of English, Oxford: Clarendon Press
  6. ^ a b c d e f g h i Simpson, J. A.; Weiner, E. S. C., eds. (1989), The Oxford English Dictionary, 2nd ed., Oxford: Clarendon Press

Related etymologies

Cite this entry

“Diameter.” Etymologically, 16 Oct. 2026, etymologically.com/en/diameter. Accessed 16 Oct. 2026.

Last edited on . ·