ra·di·ant / ˈrādēənt/ • adj. 1. sending out light; shining or glowing brightly: a bird with radiant green and red plumage. ∎  (of a person or their expression) clearly emanating great joy, love, or health: she gave him a radiant smile. ∎  (of an emotion or quality) emanating powerfully from someone or something; very intense or conspicuous: he praised her radiant self-confidence.2. (of heat) transmitted by radiation, rather than conduction or convection. ∎  (of an appliance) designed to emit such energy, esp. for cooking or heating.• n. a point or object from which light or heat radiates, esp. a heating element in an electric or gas heater.DERIVATIVES: ra·di·an·cy / -ənsē/ n.ra·di·ant·ly adv.

radiant shining brightly XV; pert. to radiation XVIII. — L. radiāns, -ant-, prp. of radiāre radiate, f. radius RAY1.
Hence radiance XVII, radi-ancy XVII. So radiate (-ATE3) emit rays XVII; spread in all directions from a centre XIX. f. radiāt-, pp. stem of L. radiāre. radiation XVII. — L. radiator one or that which radiates XIX (in sense ‘apparatus for circulating hot water to warm an apartment’ orig. U.S.).