The Collaborative International Dictionary of English v.0.48:

nematode \nem"a*tode\, a. (Zool.)
   Same as Nematoid.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

nematode \nem"a*tode\, n. (Zool.)
   Any worm of the phylum Nematoda; a roundworm; -- they are
   unsegmented worms having a cylindrical elongated body. They
   may live freely in soil or water, or as parasites in plants
   or animals.
   [PJC]

WordNet (r) 3.0 (2006):

nematode
    n 1: unsegmented worms with elongated rounded body pointed at
         both ends; mostly free-living but some are parasitic [syn:
         nematode, nematode worm, roundworm]