word-forming element meaning "earth, the Earth," ultimately from Greek geo-, combining form of Attic and Ionic gē "the earth, land, a land or country" (see Gaia).
thermal adj.
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.