from the OED online word of the day, 21 August 2011
aestivation | estivation, n.
Etymology:modern < Latin æstīvāt- participial stem of æstīvā-re (see aestivate v.), after nouns of action in -tion suffix, as if < Latin *æstīvātiōn-em. In the Bot. sense it is < modern Latin æstīvātio introduced by Linnæus. Lord Bacon spelt estivation, but the techn. spelling is commonly æstivation. As to the pronunciation of æ-, see aestival adj., and compare estimation, Latin æstimātio.
†1. The passing or spending of the summer; summer retreat or residence. Obs.
1625 Bacon Ess. (new ed.) xlv. 263 Let it be turned to a Grotta, or Place of Shade, or Estiuation.
1731 N. Bailey Universal Etymol. Eng. Dict. II, Æstivation, a dwelling or residence in a place for the summer time.
1755 Johnson Dict. Eng. Lang., Estivation, the act of passing the summer.
2. Zool. The act of remaining dormant or torpid during the dry season, or extreme heat of summer; summer-sleep. Opposed to hibernation. Also fig.
1839 C. Darwin in R. Fitzroy & C. Darwin Narr. Surv. Voy. H.M.S. Adventure & Beagle III. v. 116 Within the tropics, the hybernation, or more properly estivation, of animals is governed by the times of drought.
1870 Pall Mall Gaz. 12 Dec. 11 With what we are pleased to call the cold weather Calcutta rouses herself from her æstivation of seven long months.