The Collaborative International Dictionary of English v.0.48:

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.
      [1913 Webster]

   2. pl. (Bot.) Fine hairs on plants, resembling the pile of
      velvet.
      [1913 Webster]

WordNet (r) 3.0 (2006):

villus
    n 1: a minute hairlike projection on mucous membrane