a state of deep and often prolonged unconsciousness; usually the result of disease or injury
"After suffering a severe head injury, he slipped into a coma that lasted for several weeks before doctors finally declared him awake."
(botany) a usually terminal tuft of bracts (as in the pineapple) or tuft of hairs (especially on certain seeds)
"The botanist examined the pineapple's crown to identify the distinctive coma of leaf-like bracts at its tip."
(astronomy) the luminous cloud of particles surrounding the frozen nucleus of a comet; forms as the comet approaches the sun and is warmed
"As Halley's Comet draws closer to the Sun, its icy surface warms up and releases gas that creates a spectacular coma around the dark nucleus."
A state of unconsciousness from which one may not wake up, usually induced by some form of trauma.
"The spacecraft captured stunning images of the coma, revealing how the sun's heat vaporized ices and created a glowing envelope around the comet's icy core."
A cloud of dust surrounding the nucleus of a comet.