semidiameter

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noun

The apparent radius of a star etc, when viewed from Earth.

OriginMiddle English semidiametre ← Medieval Latin sēmidiameter →
Scrabble 17
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Meanings

nounsemidiameter (plural semidiameters)

plural semidiameters

  1. astronomyThe apparent radius of a star etc, when viewed from Earth.
  2. archaicA radius: half of a diameter.

    [B]etweene the ſphere of Saturne and the Firmament, there is ſuch an incredible and vaſt ſpace or diſtance (7000000. ſemidiameters of the earth, as Tycho [Brahe] calculates) void of ſtarres: [...]

    1638, Democritus Junior [pseudonym; Robert Burton], “Ayre Rectified. With a Digression of the Ayre.”, in The Anatomy of Melancholy. […], 5th edition, Oxford, Oxfordshire: […] [Robert Young, Miles Flesher, and Leonard Lichfield and William Turner] for Henry Cripps, →OCLC, partition 2, section 2, member 3, page 254

Origin

  1. Medieval Latinsēmidiameter
  2. Middle Englishsemidiametre
  3. Englishsemidiameter

From Middle English semidiametre, semydiametre, from Medieval Latin sēmidiameter, equivalent to semi- + diameter.

More words from Middle English, Medieval Latin

Full word history & related roots →
Cite this entry
APA

semidiameter. (n.d.). In WatkinsX Dictionary. Retrieved November 2, 2026, from https://dictionary.watkinsx.com/word/semidiameter

MLA

“semidiameter.” WatkinsX Dictionary, https://dictionary.watkinsx.com/word/semidiameter. Accessed November 2, 2026.

Chicago

WatkinsX Dictionary, s.v. “semidiameter,” accessed November 2, 2026, https://dictionary.watkinsx.com/word/semidiameter.

Source: semidiameter on Wiktionary, CC BY-SA 4.0.