The Collaborative International Dictionary of English v.0.48:

Entozoon \En`to*zo"["o]n\, n.; pl. Entozoa. [NL. See
   Entozoa.] (Zo["o]l.)
   One of the Entozoa.
   [1913 Webster]

WordNet (r) 3.0 (2006):

entozoon
    n 1: any of various parasites that live in the internal organs
         of animals (especially intestinal worms) [syn:
         endoparasite, entoparasite, entozoan, entozoon,
         endozoan]