chi·tin 
(kītn)
(kītn)n.
A nitrogen-containing polysaccharide that is a tough, protective, semitransparent substance and is the principal component of arthropod exoskeletons and the cell walls of certain fungi.
[French chitine : New Latin chitōn, mollusk (from Greek khitōn, chiton; see CHITON) + -INE2.]
chitin·ous adj.