astronomy the luminous cloud surrounding the frozen solid nucleus in the head of a comet, formed by vaporization of part of the nucleus when the comet is close to the sun
2.
botany
a. a tuft of hairs attached to the seed coat of some seeds
b. the terminal crown of leaves of palms and moss stems
3.
optics a type of lens defect characterized by the formation of a diffuse pear-shaped image from a point object
[C17: from Latin: hair of the head, from Greek komē]