The Collaborative International Dictionary of English v.0.48:

moorhen \moorhen\ n. (Zool.)
   1. A black gallinule (Gallinula chloropus) that inhabits
      ponds and lakes.

   Syn: Gallinula chloropus.
        [WordNet 1.5]

   2. The female of the moor fowl; the moor hen.
      [WordNet 1.5]

WordNet (r) 3.0 (2006):

moorhen
    n 1: black gallinule that inhabits ponds and lakes [syn:
         moorhen, Gallinula chloropus]
    2: female red grouse