c.1425, possibly from Anglo-Fr.
*dormouse "tending to be dormant" (from stem of
dormir "to sleep," see
dormer), with the second element mistaken for
mouse, or from a M.E. dial. compound of
mouse and M.Fr.
dormir. The rodent is inactive in winter. Fr.
dormeuse, fem. of
dormeur "sleeper" is only attested from 17c.