The Collaborative International Dictionary of English v.0.48:

Sleek \Sleek\ (sl[=e]k), a. [Compar. Sleeker (sl[=e]k"[~e]r);
   superl. Sleekest.] [OE. slik; akin to Icel. sl[imac]kr, and
   OE. sliken to glide, slide, G. schleichen, OHG. sl[imac]hhan,
   D. slik, slijk, mud, slime, and E. slink. Cf. Slick,
   Slink.]
   1. Having an even, smooth surface; smooth; hence, glossy; as,
      sleek hair. --Chaucer.
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            So sleek her skin, so faultless was her make.
                                                  --Dryden.
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   2. Not rough or harsh.
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            Those rugged names to our like mouths grow sleek.
                                                  --Milton.
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