What does "sleek" mean?

Sleek: Not rough or harsh. Those rugged names to our like mouths grow sleek. Milton.

Additional senses

  1. 2.With ease and dexterity. [Low]
  2. 3.That which makes smooth; varnish. [R.]
  3. 4.To make even and smooth; to render smooth, soft, and glossy; to smooth over. Sleeking her soft alluring locks. Milton. Gentle, my lord, sleek o'er your rugged looks. Shak.

Sources