exothermic (adj.)

word-forming element in words of Greek origin meaning "outer, outside, outer part," used from mid-19c. in scientific words (such as exoskeleton), from Greek exō (adv.) "outside," related to ex (prep.) "out of" (see ex-).

1756, "having to do with hot springs," from French thermal (Buffon), from Greek therme "heat, feverish heat," from PIE root *gwher- "to heat, warm." Sense of "having to do with heat" is first recorded 1837. The noun meaning "rising current of relatively warm air" is recorded from 1933.