tortoiseshell

noun

1. (uncountable, usually)The horny, translucent, mottled covering of the carapace of the hawksbill turtle, used as a veneer etc.
2. (uncountable, usually)The hawksbill turtle.
3. (uncountable, usually)A domestic cat (or a rabbit, guinea-pig, etc.) whose fur has black, brown and yellow markings.
4. (uncountable, usually)Any of several butterflies, mostly of the genera Nymphalis and Aglais that have similar markings.

adj

1. (not-comparable)Made of the covering of carapace of hawksbill turtle.
2. (not-comparable)Having markings resembling covering of carapace of hawksbill turtle.

   “Speaking of round sunglasses, these lightweight polarized ones and come in two shades of tortoiseshell as well as black and bronze.”