noun

• (countable) A backward kick; a retrograde movement of an extremity.
  "Kickbacks work the triceps muscle at the back of your arm. Exercising these muscles helps eliminate arm jiggle."
• (countable, informal) A covert, often illegal, payment in return for a favor consisting of providing an opportunity of chargeable transaction; especially, a kind of quid pro quo in which if you (an insider) secretly help me (an outsider) win the bid for the contract then I will secretly send you a portion of the contract value; thus, a kind of bribe.
  "Central to his [Yury Skuratov's] investigation were kickbacks supposedly paid by a Swiss construction company for contracts to restore government buildings, including both houses of parliament."
• (uncountable, firearms, machinery) Recoil; a sudden backward motion, usually in the direction of the operator.
• (countable, machinery) An accident where an object being cut by a rotating blade or disk, such as a circular saw, is caught by the blade and thrown outward.