The Collaborative International Dictionary of English v.0.48:

Nematoidea \Nem`a*toi"de*a\, prop. n. pl. [NL., fr. Gr. nh^ma,
   nh`matos, thread + -oid.] (Zool.)
   A phylum of worms, having a long, round, and generally smooth
   body; the roundworms. Called also Nematodea, and more
   commonly Nematoda. Formerly, it was classed as a taxonomic
   order.
   [1913 Webster +PJC]

   Note: The trichina, stomach worm, and pinworm of man belong
         to this group. See also Vinegar eel, under Vinegar,
         and Gapeworm.
         [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Nematoda \Nem`a*to"da\, prop. n. pl. (Zool.)
   A phylum of worms, having a long, round, and generally smooth
   body; the roundworms. They are mostly parasites, in plants
   and animals, but some are free-living in soil or water. Also
   called Nematoidea.
   [1913 Webster +PJC]

WordNet (r) 3.0 (2006):

Nematoda
    n 1: unsegmented worms: roundworms; threadworms; eelworms [syn:
         Nematoda, phylum Nematoda, Aschelminthes, phylum
         Aschelminthes]