chitin n.

mollusc genus, 1816, from Latinized form of Greek khiton "frock (worn by both sexes), tunic, mail coat" (see chitin). Used in English in literal sense of "ancient Greek tunic" from 1850. The molluscs also are known as coat-of-mail shells for their mail-like covering.

late 15c., from Old French tunique (12c.) or directly from Latin tunica "undergarment worn by either sex" (source of Spanish tunica, Italian tonica, Old English tunece, Old High German tunihha), probably from a Semitic source (compare Hebrew kuttoneth "coat," Aramaic kittuna). Compare chitin, from a Greek name for a similar garment, also probably from a Semitic source.