Why is the ninth month called September?
Old English -slician (in nigslicod "newly made sleek"), from Proto-Germanic *slikojan, from base *slikaz (cf. 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.
[earlier 1800s uses were in comparative phrases like slick as bear's grease and slick as molasses]
glassy patch or streak on a relatively undisturbed ocean or lake surface, formed where surface tension is reduced by a monomolecular layer of organic matter produced by plankton or by man; closer to shore most of the material is man-made hydrocarbon pollutant. Slicks are patchy when the wind velocity is less than about 13 kilometres per hour (7 knots). Winds with higher velocities break slicks into narrow, closely spaced windrows aligned parallel to the wind direction. Elongate parallel slicks may also form over and migrate with the trailing slopes of internal waves