The Collaborative International Dictionary of English v.0.48:

Roundworm \Round"worm`\, n. (Zool.)
   A nematoid worm.
   [1913 Webster]

WordNet (r) 3.0 (2006):

roundworm
    n 1: infections of the skin or nails caused by fungi and
         appearing as itching circular patches [syn: tinea,
         ringworm, roundworm]
    2: unsegmented worms with elongated rounded body pointed at both
       ends; mostly free-living but some are parasitic [syn:
       nematode, nematode worm, roundworm]