A female red grouse (a game bird) with grey plumage, or more generally, a female bird with grey coloring.
Compound from 'grey' plus 'hen,' descriptive of the female bird's appearance. In Scottish and Northern English game hunting terminology, it specifically refers to female red grouse.
Scottish hunters created specific gender terms for grouse—'greyhen' for females, 'redcock' for males—and these names are so traditional that hunting seasons are still legally organized around protecting greyhens during breeding season.
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