I. ˈtȯ(r)d.]əˌshel, -)t], ]əs(h)ˌshel\ noun
1. : a substance that forms the horny plates covering the shell of some turtles and especially the hawksbill turtle which provides almost all of the tortoiseshell of commerce and that is rich brown mottled with yellow, readily molded and welded when hot, and used in inlaying and in making ornamental articles
2. or tortoiseshell butterfly : any of several brilliantly colored butterflies of the genus Nymphalis ; especially : either of two such butterflies ( N. milberti and N. j-album ) that in the larval state feed upon nettles
II. adjective
: made of tortoise shell or having a mottled coloration suggesting tortoise shell