Meaning

noun a state of deep and often prolonged unconsciousness; usually the result of disease or injury

noun (botany) a usually terminal tuft of bracts (as in the pineapple) or tuft of hairs (especially on certain seeds)

noun (astronomy) the luminous cloud of particles surrounding the frozen nucleus of a comet; forms as the comet approaches the sun and is warmed

originLearned borrowing from Latin coma (“hair of the head”), from Ancient Greek κόμη (kómē, “hair”).

Etymology from Wiktionary, CC BY-SA 3.0