kickback (n.)

also kick-back, "mechanical reaction in an engine," from 1905 in various mechanical senses, from the verbal phrase (1895); see kick (v.) + back (adv.). By 1926 the verbal phrase was being used in a slang sense of "be forced to return pelf, pay back to victims," which was extended to illegal partial give-backs of government-set wages that were extorted from workers by employers. Hence the noun in the sense of "illegal or improper payment" (1932). The verbal phrase in the sense "make oneself comfortable, prepare to relax" is from 1975.