Source : Webster's Revised Unabridged Dictionary (1913)

Villi \Vil"li\, n.,
   pl. of {Villus}.

Villus \Vil"lus\, n.; pl. {Villi}. [L., shaggy hair, a tuft of
   hair.]
   1. (Anat.) One of the minute papillary processes on certain
      vascular membranes; a villosity; as, villi cover the
      lining of the small intestines of many animals and serve
      to increase the absorbing surface.

   2. pl. (Bot.) Fine hairs on plants, resembling the pile of
      velvet.

Source : WordNet®

villus
     n : a minute hairlike projection on mucous membrane
     [also: {villi} (pl)]

villi
     See {villus}