grouse (n.)

type of game bird, 1530s, grows (plural, used collectively), of unknown origin, possibly from Latin or Welsh. Originally the moorhen of the British Isles; later the name was extended to similar birds in other places.

"complain," 1885 (implied in agent noun grouser), British Army slang, of uncertain origin. OED notes "a curious resemblance" to Normandy French dialectal groucer, from Old French groucier, grocier "to murmur, grumble, complain," which is of imitative origin (compare Greek gru "a grunt," gruzein "to grumble;" also see grutch). Related: Groused; grousing. As a noun from 1918, from the verb.