Definify.com
Webster 1913 Edition
Coma
‖
Co′ma
,Noun.
 [L., hair, fr. Gr. 
κόμη
.] 1. 
(Astron.) 
The envelope of a comet; a nebulous covering, which surrounds the nucleus or body of a comet. 
2. 
(Bot.) 
A tuft or bunch, – as the assemblage of branches forming the head of a tree; or a cluster of bracts when empty and terminating the inflorescence of a plant; or a tuft of long hairs on certain seeds. 
Coma Berenices 
[L.] 
(Astron.)
, a small constellation north of Virgo; – called also 
 Berenice’s Hair
.Webster 1828 Edition
Coma
COMA
,Noun.
  COMA
, n.1.
  In botany, a species of bracte, terminating the stem of a plant, in a tuft or bush; as in crown-imperial.2.
  In astronomy, hairiness; the hairy appearance that surrounds a comet, when the earth or the spectator is between the comet and the sun.