"heat-resistant, impervious to radiant heat," 1839, from a- (3) "not, without" + Greek thermainein "impart heat," from thermos "hot" (see thermal).
Entries linking to athermanous
a- 3
prefix meaning "not, without," from Greek a-, an- "not" (the "alpha privative"), from PIE root *ne- "not" (source also of English un-).
In words from Greek, such as abysmal, adamant, amethyst; also partly nativized as a prefix of negation (asexual, amoral, agnostic). The ancient alpha privatum, denoting want or absence.
Greek also had an alpha copulativum, a- or ha-, expressing union or likeness, which is the a- expressing "together" in acolyte, acoustic, Adelphi, etc. It is from PIE root *sem- (1) "one; as one, together with."
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.