dormouse (n.)

long-tailed Old World rodent noted for its state of semi-hibernation in winter, early 15c., possibly from Anglo-French *dormouse "tending to be dormant" (from stem of dormir "to sleep," see dormant), with the second element mistaken for mouse; or perhaps it is from a Middle English dialectal compound of mouse (n.) and Middle French dormir. French dormeuse, fem. of dormeur "sleeper" is attested only from 17c.