thermal

Universal Words adjective, noun adjective [onlybeforenoun] 1 (technical) connected with heat: thermal energy / insulation 2 (of clothing) designed to keep you warm by preventing heat from escaping from the body: thermal underwear 3 (of streams, lakes, etc.) in which the water has been naturally heated by the earth: thermal springs thermally adverb noun 1 [C] a rising current of warm air used, for example, by a GLIDER to gain height 2 (thermals) [pl.] (especially BrE) warm underwear that prevents heat from escaping from the body