Source : Webster's Revised Unabridged Dictionary (1913)

AEstivation \[AE]s`ti*va"tion\, n.
   1. (Zo["o]l.) The state of torpidity induced by the heat and
      dryness of summer, as in certain snails; -- opposed to
      {hibernation}.

   2. (Bot.) The arrangement of the petals in a flower bud, as
      to folding, overlapping, etc.; prefloration. --Gray.
      [Spelt also {estivation}.]

Source : WordNet®

aestivation
     n 1: (zoology) cessation or slowing of activity during the
          summer; especially slowing of metabolism in some animals
          during a hot or dry period [syn: {estivation}]
     2: (botany) the arrangement of sepals and petals in a flower
        bud before it opens [syn: {estivation}]