noun.
A parasite, such as a tapeworm, that lives within another organism.
The Century Dictionary and Cyclopedia
noun.
An internal parasite; a parasite which lives in the internal parts or organs of the host, as distinguished from an ectoparasite, which infests the skin or surface. The entozoans are of this character. The term has no classificatory meaning.
the GNU version of the Collaborative International Dictionary of English
noun.
Any parasite which lives in the internal organs of an animal, as the tapeworms, Trichina, etc.; -- opposed to ectoparasite. See entozoön.