Source : Webster's Revised Unabridged Dictionary (1913)

AEstivate \[AE]s"ti*vate\, v. i. [L. aestivare, aestivatum.]
   1. To spend the summer.

   2. (Zo["o]l.) To pass the summer in a state of torpor. [Spelt
      also {estivate}.]

Source : WordNet®

aestivate
     v : sleep during summer; "certain animals estivate" [syn: {estivate}]
         [ant: {hibernate}, {hibernate}]