A usually terminal tuft of hairs especially on a seed.

In medicine, a state of deep unconsciousness from which the subject cannot be roused. Possible causes include head injury, brain disease, liver failure, cerebral hemorrhage, and drug overdose.
A state of deep and often prolonged unconsciousness; usually the result of disease or injury; SYN. comatoseness.

In optics, one of the geometrical aberrations of a lens, whereby skew rays from a pointed object make a comet-shaped spot on the image plane instead of meeting at a point.

In astronomy, the hazy cloud of gas and dust that surrounds the nucleus of a comet.
(Astronomy) The luminous cloud of particles surrounding the frozen nucleus of a comet; forms as the comet approaches the sun and is warmed.