The Collaborative International Dictionary of English v.0.48:

Polypus \Pol"y*pus\, n.; pl. E. Polypuses, L. Polypi. [L.
   See Polyp.]
   1. (Zool.) Same as Polyp.
      [1913 Webster]

   2. (Med.) A tumor, usually with a narrow base, somewhat
      resembling a pear, -- found in the nose, uterus, etc., and
      produced by hypertrophy of some portion of the mucous
      membrane.
      [1913 Webster]

WordNet (r) 3.0 (2006):

polypus
    n 1: a small vascular growth on the surface of a mucous membrane
         [syn: polyp, polypus]