Wordnet 3.0
NOUN (1)
1.
a tough semitransparent horny substance;
the principal component of the exoskeletons of arthropods and the cell walls of certain fungi;
The Collaborative International Dictionary of English v.0.48:
Chitin \Chi"tin\, n. [See Chiton.] (Chem.)
A white amorphous horny substance forming the harder part of
the outer integument of insects, crustacea, and various other
invertebrates; entomolin.
[1913 Webster]
WordNet (r) 3.0 (2006):
chitin
n 1: a tough semitransparent horny substance; the principal
component of the exoskeletons of arthropods and the cell
walls of certain fungi