The Collaborative International Dictionary of English v.0.48:

Polypodium \Pol"y*po`di*um\, n. [L., fr. Gr. ?, dim. of ?. See
   Polyp, and cf. 2d Polypode.] (Bot.)
   A genus of plants of the order Filices or ferns. The
   fructifications are in uncovered roundish points, called
   sori, scattered over the inferior surface of the frond or
   leaf. There are numerous species.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Polypodium
    n 1: a genus of ferns belonging to the family Polypodiaceae and
         having rounded naked sori [syn: Polypodium, genus
         Polypodium]