kelh₂-mn̥-
“heated chamber, warm room”calm, cauldron
Nominal of *kelh₂- giving Latin calor, English calm, cauldron from heated-room sense.
Discussion
The PIE form *kelh₂-mn̥- (heated chamber, warm room) derives from *kelh₂- (to be warm, to heat), with the result noun suffix *-mn̥-. The literal meaning is "the heated thing" — a room or space defined by its warmth, in contrast to the cold outside.
Latin calor (heat, warmth) and the derivative calidus (warm, hot) continue the root transparently: calorie (a unit of heat), caldron/cauldron (a heated vessel), and scald (from Latin excaldāre, "to wash in hot water"). The medical term caloric and the geographic term Caledonia (possibly "hard/warm land," though this is debated) extend the family.
The specific *-mn̥- formation gave Latin camīnus (furnace, forge, fireplace) via a different developmental path, which entered English as chimney (via Old French cheminée) — the chimney is etymologically the heated chamber itself, not just the flue. In modern English the word has narrowed to the exhaust structure, but the original sense of "heated room" survives in the French cheminée (fireplace, mantelpiece) and Italian caminetto (fireplace).
German Kammer (chamber, room) may be connected through a different formation of the same root, though some scholars derive it from Latin camera (vaulted room) instead. The overlap between the "warm room" and the "chamber" concepts reflects the practical reality of northern European dwellings: the heated room WAS the chamber — the one room with a fire.
The root *kelh₂- itself, distinct from *kelh₁- (to call/shout), is identified by the h₂ laryngeal, which produces a-colouring in the daughter languages. The distinction between the two identically-shaped but semantically different roots — one for heat, one for calling — is maintained by the laryngeal evidence: Latin calor (heat, with a-vowel from *h₂) versus Latin calāre (to call, also with a-vowel but from *h₁ — the apparent identity is coincidental in Latin but distinguishable in other branches).
Old English calan (to be cold — with a reversed sense, from the concept of being away from the heat source) may be distantly connected, though this etymology is contested. Lithuanian šìlti (to become warm) provides Baltic attestation.