Etymograph

English

irradiate

Irradiate comes from Medieval Latin irradiātus, from Latin radiō ‘to cause to radiate, irradiate’, and ultimately from radius ‘ray of light’.

  1. Latinc. 75 BCE–200 CEradius1‘ray of light’
  2. Latinc. 75 BCE–200 CEradiō1‘to cause to radiate, irradiate’
  3. Medieval Latinc. 600–1500irradiātus1
  4. Middle Englishc. 1150–1500irradiate1‘illuminated, shining’
  5. Englishearliest quotation 1725irradiate1

attested reconstructed ? uncertain or disputed deepest recorded ancestor

  1. 1 Wiktionary, English irradiate
  2. Earliest quotation in Wiktionary’s entry: 1725, Homer, Book X: “There ſeek the Theban Bard, depriv'd of ſight, /…”.

Earlier history uncertain. See Wiktionary.

Lineage

  1. Latinc. 75 BCE–200 CEradiusWiktionary, English irradiate‘ray of light’
  2. Latinc. 75 BCE–200 CEradiōWiktionary, English irradiate‘to cause to radiate, irradiate’
  3. Medieval Latinc. 600–1500irradiātusWiktionary, English irradiate
  4. Middle Englishc. 1150–1500irradiateWiktionary, English irradiate‘illuminated, shining’
  5. Englishearliest quotation 1725irradiateWiktionary, English irradiate. Earliest quotation in Wiktionary’s entry: 1725, Homer, Book X: “There ſeek the Theban Bard, depriv'd of ſight, /…”

Formed from in- ‘against’ + radiate

Proto-Indo-European *h₁én ‘in’

Proto-Germanic *in ‘into’

English in-

Latin radius ‘spoke of a wheel’

Latin radiō ‘to radiate, furnish with spokes, give out…’

Latin radiātus ‘radiated’

English radiate

The story

From Middle English irradiate (‘illuminated, shining’), borrowed from Medieval Latin irradiātus, perfect passive participle of irradiō, from ir- (‘against; into; on, upon’) + radiō (‘to cause to radiate, irradiate; to emit beams, radiate’), from radius (‘ray of light; rod, staff; spoke of a wheel’) + -ō (first conjugation verb-forming suffix) (further etymology uncertain; possibly ultimately from Proto-Indo-European *reh₁t- (‘beam; pole; post’)).uncertain The source flags this step as uncertain. The adjective is attested earlier than the verb. The English word is analysable as in- (‘against; into; on, upon’) + radiate.

Full etymology on Wiktionary

Linked words

through Latin radius ‘ray of light’

ray, radius, rayon, radial, 7 more

through Latin radiō ‘to cause to radiate, irradiate’

laser, radiation, radiant, 2 more

Another origin of irradiate

  1. Middle Englishc. 1150–1500irradiate‘illuminated, shining’
  2. Englishtodayirradiate

Today it means

adj Made brilliant or bright; irradiated, illuminated.

Sources

Sources: Wiktionary, “irradiate”. By Wiktionary contributors, CC BY-SA 4.0, via kaikki.org (dump of Oct 3 2026); text adapted and restructured. Language periods are conventional ranges, not dates for this word. License.

Etymograph / Latin radius / irradiate

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