The Collaborative International Dictionary of English v.0.48:

Hibernacle \Hi*ber"na*cle\, n. [L. hibernaculum a winter
   residence, pl. hibernacula winter quarters: cf. F.
   hibernacle. See Hibernate.]
   That which serves for protection or shelter in winter; winter
   quarters; as, the hibernacle of an animal or a plant.
   --Martyn.
   [1913 Webster]