1610s, "issue or spread in all directions from a point in rays or straight lines," from Latin radiatus, past participle of radiare "to beam, shine, gleam; make beaming," from radius "beam of light; spoke of a wheel" (see radius). Meaning "be radiant, give off rays (of light or heat)" is from 1640s. Related: Radiated; radiates; radiating.
"having rays, furnished with rays or ray-like parts, shining," 1660s, from Latin radiatus, past participle of radiare "to beam, shine, gleam; make beaming," from radius "beam of light; spoke of a wheel" (see radius).
1832, "any thing which radiates," agent noun in Latin form from radiate (v.). Originally a stove-like apparatus, as a device designed to communicate heat from steam to a room by 1855; the sense of "cooling device in an internal combustion engine" is by 1899.
principal Hindu sacred book, 1776, Reig Beid, from Sanskrit rigveda, from rg- "praise, hymn, spoken stanza," literally "brightness" (from PIE *erkw- "to radiate, beam; praise") + veda "knowledge" (from PIE *weid-o-, from root *weid- "to see"). A thousand hymns, orally transmitted, probably dating from before 1000 B.C.E. Related: Rig-vedic.