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.
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