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Webster 1913 Edition

Noun.

[L.

tetrao

a heath cock, grouse, Gr. [GREEK]: cf. F.

tétraonide

(Zool.)

A bird belonging to the tribe of which the genus

Tetrao

is the type, as the grouse, partridge, quail, and the like. Used also adjectively.

tetraonid ‎(plural tetraonids)

(zoology) A bird belonging to the tribe of which the genus Tetrao is the type.
The grouse, partridge and quail are tetraonids.