Source : Webster's Revised Unabridged Dictionary (1913)

Pinworm \Pin"worm`\, n. (Zo["o]l.)
   A small nematoid worm ({Oxyurus vermicularis}), which is
   parasitic chiefly in the rectum of man. It is most common in
   children and aged persons.

Source : WordNet®

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