1660s, "action of passing the winter" (of plants, insect eggs, etc.), from Latin hibernationem (nominative hibernatio) "the action of passing the winter," noun of action from past participle stem of hibernare "to winter, pass the winter, occupy winter quarters;" related to hiems "winter," from PIE root *gheim- "winter." Meaning "dormant condition of animals" is from 1789.

Proto-Indo-European root meaning "winter." 

It forms all or part of: chimera; chiono-; hiemal; hibernacle; hibernal; hibernate; hibernation; Himalaya.

It is the hypothetical source of/evidence for its existence is provided by:  Sanskrit heman "in winter;" Hittite gimmant-, Armenian jmern, Greek kheima, Latin hiems, Old Church Slavonic zima, Lithuanian žiema "winter;" Greek khion "snow."

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 French dormir. French dormeuse, fem. of dormeur "sleeper" is attested only from 17c.