The Collaborative International Dictionary of English v.0.48:

Threadworm \Thread"worm`\, n. (Zool.)
   Any long, slender nematode worm, especially the pinworm and
   filaria.
   [1913 Webster]

WordNet (r) 3.0 (2006):

threadworm
    n 1: small threadlike worm infesting human intestines and rectum
         especially in children [syn: pinworm, threadworm,
         Enterobius vermicularis]