1520s, "to move confusedly" (intransitive), perhaps coined on model of stumble, tumble, etc., and onomatopoeic or felt as suggestive of the action indicated. Transitive meaning "mix in a confused mass" is from 1540s. In 17c. it was yet another euphemism for "have sex with" (a sense first attested 1580s). Related: Jumbled; jumbling.