NOUN (3)

1. the torpid or resting state in which some animals pass the winter;

2. cessation from or slowing of activity during the winter; especially slowing of metabolism in some animals;

3. the act of retiring into inactivity;
- Example: "he emerged from his hibernation to make his first appearance in several years"

The Collaborative International Dictionary of English v.0.48:

Hibernation \Hi`ber*na"tion\, n. [Cf. F. hibernation.]
   The act or state of hibernating. --Evelyn.
   [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

36 Moby Thesaurus words for "hibernation":
   beauty sleep, beddy-bye, bedtime, blanket drill, bye-bye, dormancy,
   doze, dreamland, drowse, fitful sleep, immobility, inaction,
   inactiveness, inactivity, inertia, land of Nod, light sleep, lull,
   motionlessness, quiescence, repose, shut-eye, silken repose, sleep,
   sleepland, sleepwalking, slumber, slumberland, snoozle,
   somnambulism, somniloquy, somnus, suspension, unconsciousness,
   underactivity, winter sleep