an informal short form of tortoiseshell (sense 3), tortoiseshell (sense 6b)
tortoiseshell in British English
(ˈtɔːtəsˌʃɛl)
noun
1.
a horny translucent yellow-and-brown mottled substance obtained from the outer layer of the shell of the hawksbill turtle: used for making ornaments, jewellery, etc
2.
a similar synthetic substance, esp plastic or celluloid, now more widely used than the natural product
3. Also called: tortoiseshell cat
a breed of domestic cat, usually female, having black, cream, and brownish markings
4.
any of several nymphalid butterflies of the genus Nymphalis, and related genera, having orange-brown wings with black markings