1. [noun] A state of sleep from which one may not wake up, usually induced by some form of trauma.
2. [noun] (astronomy) A cloud of dust surrounding the nucleus of a comet.
3. [noun] (optics) A defect characterized by diffuse, pear-shaped images that should be points.
4. [noun] (botany) A tuft or bunch, such as the assemblage of branches forming the head of a tree, a cluster of bracts when empty and terminating the inflorescence of a plant, or a tuft of long hairs on certain seeds.
5. [noun] A state of deep and often prolonged unconsciousness; usually the result of disease or injury.
6. [noun] (botany) a usually terminal tuft of bracts (as in the pineapple) or tuft of hairs (especially on certain seeds).
7. [noun] (astronomy) the luminous cloud of particles surrounding the frozen nucleus of a comet; forms as the comet approaches the sun and is warmed.
