Source : Webster's Revised Unabridged Dictionary (1913)

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}.]
   (Zo["o]l.)
   (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}.]

   {Fresh-water polyp}, the hydra.

   {Polyp stem} (Zo["o]l.), that portion of the stem of a
      siphonophore which bears the polypites, or feeding zooids.

Source : WordNet®

polyp
     n 1: a small vascular growth on the surface of a mucous membrane
          [syn: {polypus}]
     2: one of two forms that coelenterates take e.g. a hydra or
        coral: usually sedentary and has a hollow cylindrical body
        usually with a ring of tentacles around the mouth