Etymology
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irradiate (v.)
c. 1600, "to cast beams of light upon," from Latin irradiatus, past participle of irradiare "shine forth, beam upon, illumine," from assimilated form of in- "into, in" (from PIE root *en "in") + radiare "to shine" (see radiate (v.)). Meaning "expose to radiation other than light" (originally X-rays) is from 1901. Related: Irradiated; irradiating.
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irradiant (adj.)
1520s, from Latin irradiantem (nominative irradians), present participle of irradiare "to shine forth" (see irradiate). Related: Irradiantly.
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irradiance (n.)
1660s, from Latin irradiantem (nominative irradians), present participle of irradiare "to shine forth" (see irradiate). Related: Irradiancy (1640s).
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irradiation (n.)
1580s, in reference to light (literally and figuratively), from French irradiation, noun of action from past participle stem of Latin irradiare (see irradiate). Of X-rays, etc., from 1901.
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