Английский Этимологический словарь - slick (v.)

- O.E. -slician (attested in nigslicod "newly made sleek"), from P.Gmc. *slikojanan, from base *slikaz. The adj. in the sense of "clever in deception" is first recorded 1599; as an adv., c.1300. Slicker "waterproof raincoat" first recorded 1884; sense of "clever and crafty person" is from 1900.