Standard Lemma guide

radian

noun · 2 senses · updated from the 2026-07-25 local source snapshot

Definitions and examples are grouped by meaning. Pronunciation, history, word forms, translations, descendants, synonyms, antonyms, derived terms, and related words appear whenever the source provides them.

Sound

Pronunciation

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  • /ˈɹeɪdiən/
  • Southern-England: Recorded audio is listed in the source snapshot.
  • rhymes with -eɪdiən

1

noun

Meaning 1

In the International System of Units, the derived unit of plane angle: the angle subtended at the centre of a circle by an arc of its circumference equal in length to the radius of the circle.

Definition source: English Wiktionary via Wiktextract

Topics: geometry, mathematics, sciences

No example sentence was provided for this meaning.

Meaning relationships

Synonyms: none provided

Antonyms: none provided

2

noun

Meaning 2

the unit of plane angle adopted under the Systeme International d'Unites; equal to the angle at the center of a circle subtended by an arc equal in length to the radius (approximately 57.295 degrees)

Definition source: Princeton WordNet 3.0

No example sentence was provided for this meaning.

Meaning relationships

Synonyms: rad

Antonyms: none provided

Broader terms: angular unit

History

Etymology

Etymology tree Latin radiusbor. English radius Proto-Indo-European *-nós Proto-Italic *-nos Latin -nus Latin -ānus Old French -ainder. Middle English -an English -an English radian From radius + -an.

Across languages

Translations

29 source translations are retained for this English entry.

  • Asturian: radián — unit
  • Bulgarian: радиан (radian) — unit
  • Catalan: radiant — unit
  • Catalan: radian — unit
  • Chinese Mandarin: 弧度 (húdù) — unit
  • Dutch: radiaal — unit
  • Finnish: radiaani — unit
  • French: radian — unit
  • Galician: radián — unit
  • German: Radiant — unit
  • Greek: ακτίνιο (aktínio) — unit
  • Indonesian: radian — unit
  • Irish: raidian — unit
  • Italian: radiante — unit
  • Japanese: ラジアン (rajian) — unit
  • Latvian: radiāns — unit
  • Malay: radian — unit
  • Polish: radian — unit
  • Portuguese: radiano — unit
  • Romanian: radian — unit
  • Russian: радиан (radian) — unit
  • Slovak: radián — unit
  • Slovene: radian — unit
  • Spanish: radián — unit
  • Swedish: radian — unit
  • Tagalog: radyan — unit
  • Thai: เรเดียน (ree-dîian) — unit
  • Turkish: radyan — unit
  • Welsh: radian — unit