The Collaborative International Dictionary of English v.0.48:

Coma \Co"ma\, n. [L., hair, fr. Gr. ko`mh.]
   1. (Astron.) The envelope of a comet; a nebulous covering,
      which surrounds the nucleus or body of a comet.
      [1913 Webster]

   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.
      [1913 Webster]

   Coma Berenices[L.] (Astron.), a small constellation north
      of Virgo; -- called also Berenice's Hair.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Coma Berenices
    n 1: a constellation in the northern hemisphere between Ursa
         Major and Bootes; contains a cluster of some 10,000
         galaxies