The Collaborative International Dictionary of English v.0.48:

Grouse \Grouse\ (grous), n. sing. & pl. [Prob. after the analogy
   of mouse, mice, fr. the earlier grice, OF. griesche meor hen:
   cf. F. piegri[`e]che shrike.] (Zool.)
   Any of the numerous species of gallinaceous birds of the
   family Tetraonid[ae], and subfamily Tetraonin[ae],
   inhabiting Europe, Asia, and North America. They have plump
   bodies, strong, well-feathered legs, and usually mottled
   plumage. The group includes the ptarmigans (Lagopus),
   having feathered feet.
   [1913 Webster]

   Note: Among the European species are the red grouse (Lagopus
         Scoticus) and the hazel grouse (Bonasa betulina).
         See Capercaidzie, Ptarmigan, and Heath grouse.
         Among the most important American species are the
         ruffed grouse, or New England partridge (Bonasa
         umbellus); the sharp-tailed grouse (Pedioc[ae]tes
         phasianellus) of the West; the dusky blue, or pine
         grouse (Dendragapus obscurus) of the Rocky Mountains;
         the Canada grouse, or spruce partridge (D.
         Canadensis). See also Prairie hen, and Sage cock.
         The Old World sand grouse (Pterocles, etc.) belong to
         a very different family. See Pterocletes, and Sand
         grouse.
         [1913 Webster]