sleek adj.

"smooth, glossy, soft" (of body parts, hair, skin, etc.), by 1580s, a variant of Middle English slike "sleek, smooth" (see slick (adj.)). Originally of healthy-looking animal hair (Shakespeare, of Bottom with his ass's head); applied to persons 1630s, with a sense of "plump and smooth-skinned." The figurative meaning in reference to persons or personalities, "slick, fawning, flattering," is from 1590s.

The form slick is related to sleek much as crick (n.2) is related to creek (n.), but is in fact the more orig. form, until recently in good literary use, and still common in colloquial use (the word being often so pronounced even though spelled sleek), but now regarded by many as somewhat provincial ... [Century Dictionary, 1895]

"make smooth and glossy on the surface," mid-15c., sleken, a variant of slick (v.), glossing Latin licibricinnulo; also see sleek (adj.). Related: Sleeked; sleeking. Alternative sleeken is by 1620s.