The Collaborative International Dictionary of English v.0.48:

Polyp \Pol"yp\, n. [L. polypus, Gr. ?, ?, literally,
   many-footed; poly`s many + ?, ?, foot: cf. F. polype. See
   Poly- and Foot, and cf. Polypode, Polypody, Poulp.]
   (Zool.)
   (a) One of the feeding or nutritive zooids of a hydroid or
       coral.
   (b) One of the Anthozoa.
   (c) pl. Same as Anthozoa. See Anthozoa, Madreporaria,
       Hydroid. [Written also polype.]
       [1913 Webster]

   Fresh-water polyp, the hydra.

   Polyp stem (Zool.), that portion of the stem of a
      siphonophore which bears the polypites, or feeding zooids.
      [1913 Webster]

WordNet (r) 3.0 (2006):

polyp
    n 1: a small vascular growth on the surface of a mucous membrane
         [syn: polyp, polypus]
    2: one of two forms that coelenterates take (e.g. a hydra or
       coral): usually sedentary with a hollow cylindrical body
       usually with a ring of tentacles around the mouth; "in some
       species of coelenterate, polyps are a phase in the life cycle
       that alternates with a medusoid phase"

Moby Thesaurus II by Grady Ward, 1.0:

70 Moby Thesaurus words for "polyp":
   abdominal hernia, abscess, aposteme, bed sore, blain, bleb,
   blister, boil, bubo, bulla, bunion, canker, canker sore, carbuncle,
   chancre, chancroid, chilblain, cold sore, colitis, diverticulitis,
   diverticulosis, duodenal ulcer, duodenitis, eschar,
   esophagal ulcer, esophagitis, felon, fester, festering,
   fever blister, fistula, furuncle, furunculus, gastritis, gathering,
   gumboil, hemorrhoids, hiatal hernia, kibe, lesion, megacolon,
   papula, papule, paronychia, parulis, peptic ulcer, peritonitis,
   petechia, piles, pimple, pock, pustule, rising, scab, soft chancre,
   sore, stigma, stomach ulcer, sty, suppuration, swelling, tubercle,
   ulcer, ulceration, wale, welt, wheal, whelk, whitlow, wound