Slick means smooth or slippery, but it can also describe a smooth, effortless style. How did that Girl Scout talk you into buying so many boxes of cookies? It must have been her slick sales pitch.
A great salesman is often described as slick — he or she seems more like a friend than someone trying to sell you something. Things that are smooth and glossy can also be called slick, like the surface of a glass table or an icy patch on the sidewalk. Slick is also a verb, meaning "to smooth," like when you slick back your hair. The oldest meaning of slick is shiny, and in the 1620s, it was even the name of a kind of cosmetic.