Old English -slician (in nigslicod "newly made sleek"), from Proto-Germanic *slikojan, from base *slikaz (source also of Old Norse slikr "smooth," Old High German slihhan "to glide," German schleichen "to creep, crawl, sneak," Dutch slijk "mud, mire"), from PIE *sleig- "to smooth, glide, be muddy," from root *(s)lei- "slimy" (see slime (n.)). Related: Slicked; slicking.
1620s, a kind of cosmetic, from slick (v.). Meaning "smooth place on the surface of water caused by oil, etc." is attested from 1849. Meaning "a swindler, clever person" is attested from 1959.
early 14c., "smooth, glossy, sleek" (of skin or hair); sense of "clever in deception" is first recorded 1590s; that of "first-class, excellent" is from 1833. Related: Slickly; slickness.