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]