grouse (n.) Look up grouse at Dictionary.com
type of game bird, 1530s, grows (plural, used collectively), of unknown origin, possibly from Latin or Welsh.
grouse (v.) Look up grouse at Dictionary.com
"complain," 1885 (implied in grouser), British Army slang, of uncertain origin but perhaps from Norman French dialectal groucer, from Old French groucier "to murmur, grumble," of imitative origin (compare Greek gru "a grunt," gruzein "to grumble"). Related: Groused; grousing. As a noun from 1918, from the verb.