Source : Webster's Revised Unabridged Dictionary (1913)

Estival \Es"ti*val\, a., Estivate \Es"ti*vate\, v. i.,
Estivation \Es`ti*va"tion\, n.
   Same as {[AE]stival}, {[AE]stivate}, etc.

Source : WordNet®

estivation
     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: {aestivation}]
     2: (botany) the arrangement of sepals and petals in a flower
        bud before it opens [syn: {aestivation}]