Old English brocc "badger," a borrowing from Celtic (compare Old Irish brocc, Welsh broch), from Proto-Celtic *brokkos. After c. 1400, often with the adjective stinking and meaning "a low, dirty fellow.
Entries linking to brock
badger n.
type of low, nocturnal, burrowing, carnivorous animal, 1520s, perhaps from bage "badge" (see badge) + reduced form of -ard "one who carries some action or possesses some quality," suffix related to Middle High German -hart "bold" (see -ard). If so, the central notion is the badge-like white blaze on the animal's forehead (as in French blaireau "badger," from Old French blarel, from bler "marked with a white spot;" also obsolete Middle English bauson "badger," from Old French bauzan, literally "black-and-white spotted"). But blaze (n.2) was the usual word for this.
An Old English name for the creature was the Celtic borrowing brock; also græg (Middle English grei, grey). In American English, the nickname of inhabitants or natives of Wisconsin by 1833.