'tortoiseshell' originates from English, specifically formed as a compound of the words 'tortoise' and 'shell', where 'tortoise' referred to the reptile and 'shell' meant the hard protective covering.

'tortoiseshell' developed in Early Modern English as a compound describing the shell of a tortoise (and later applied to material from certain sea turtles); usage broadened to denote both the decorative material and the characteristic mottled pattern.

Initially, it referred simply to the shell of a tortoise or turtle; over time it came to mean the decorative material made from certain turtle shells and, by extension, a mottled brown-and-black pattern.