/ ˈθɜːml; NAmE ˈθɜːrml/ adjective , noun
■ adjective [ only before noun ]
1.
( technical ) connected with heat :
thermal energy
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
► ther·mal·ly / -əli; NAmE / 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
••
WORD ORIGIN
mid 18th cent. (in the sense relating to hot springs ): from French , from Greek thermē heat.