tortoise n.

1550s, altered (perhaps by influence of porpoise) from Middle English tortuse (late 15c.), tortuce (mid-15c.), tortuge (late 14c.), from Medieval Latin tortuca (mid-13c.), perhaps from Late Latin tartaruchus "of the underworld" (see Tartarus). Others propose a source in Latin tortus "twisted," based on the shape of the feet. The classical Latin word was testudo, from testa "shell." First record of tortoise shell as a pattern of markings is from 1782.