I. ther ‧ mal 1 /ˈθɜːm ə l $ ˈθɜːr-/ BrE AmE adjective [only before noun]
[ Date: 1700-1800 ; Language: Greek ; Origin: therme ; ⇨ ↑ therm ]
1 . relating to or caused by heat:
thermal energy
2 . thermal clothing is made from special material to keep you warm in very cold weather:
thermal underwear
3 . thermal water is heated naturally under the earth:
thermal springs
II. thermal 2 BrE AmE noun
1 . [countable] a rising current of warm air used by birds
2 . thermals [plural] British English informal special warm clothing, especially underwear, worn under your other clothes