There was a table set out under a tree in front of the house, and the March Hare and the Hatter were having tea at it: a Dormouse was sitting between them, fast asleep, and the other two were using it as a cushion, resting their elbows on it, and talking over its head. “Very uncomfortable for the Dormouse,” thought Alice; ”only, as it’s asleep, I suppose it doesn’t mind.” —Lewis Carroll. Alice’s Adventures in Wonderland. Chapter VII. A Mad Tea-Party.
Technically, the dormouse is a small omnivorous rodent, a native of Eurasia and Africa, of the family the family Gliridae. The dormouse featured in Lewis Caroll’s The Adventures of Alice in Wonderland is almost certainly meant to be the British Hazel dormouse, Muscardinus avellanarius. Dormice that live in temperate regions like Britain hibernate, sometimes for as much as half the year, depending on local conditions. They may occasionally wake just long enough to snack on edibles they’ve hidden near their burrow, but then it’s back to sleep again.
The etymology isn’t exactly clear. The AHD offers:
Middle English, perhaps alteration (influenced by mous, mouse) of Anglo-Norman *dormeus, inclined to sleep, hibernating, from Old French dormir, to sleep; see DORMANT.
First, the easy part; the Middle English forms of dormouse dormoise (Middle English Dictionary Entry ) and dormowse, dormows (OED) are ostensibly derived from Anglo-Norman *dormeus, itself deriving from Old French dormir “To Sleep.”
While this is a perfectly reasonable etymology for a creature known for its sleeping patterns, it’s a problem because the supposed Anglo-Norman form *dormeus doesn’t appear to actually exist; it’s a hypothetical form. As the OED points out,
The French dormeuse, feminine of dormeur “sleeper,” sometimes suggested as the etymon, is not known before 17th cent. (s.v. dormouse).
What does seem clear is that the –mos ending of the Middle English forms, and likely, the Anglo-Norman and Old French forms, sounded to English ears like mouse, and thus a perfect name for a mouse-like creature.
The dormouse (dormice in plural) is currently endangered in Britain (including Wales), in part because of climate change; as the temperatures during the dormouse’s usual hibernation time rise, the dormouse fails to hibernate, and consequently uses up its stored fat before spring arrives and provides new food.
You can learn more about dormouse at dormice.org.