early 13c., "hook-shaped instrument or weapon," from Old Norse krokr "hook, corner," cognate with Old High German kracho "hooked tool," of obscure origin but perhaps related to a widespread group of Germanic kr- words meaning "bent, hooked." Meaning "swindler" is American English, 1879, from crooked in figurative sense of "dishonest" (1708). Crook "dishonest trick" was in Middle English.