1. 
[syn: aestival, estival]
The Collaborative International Dictionary of English v.0.48:
AEstival \[AE]s"ti*val\, a. [L. aestivalis, aestivus, fr. aestas
   summer.]
   Of or belonging to the summer; as, [ae]stival diseases.
   [Spelt also estival.]
   [1913 Webster]
The Collaborative International Dictionary of English v.0.48:
Estival \Es"ti*val\, a., Estivate \Es"ti*vate\, v. i.,
Estivation \Es`ti*va"tion\, n.
   Same as [ae]stival, [ae]stivate, etc.
   [1913 Webster]
WordNet (r) 3.0 (2006):
estival
    adj 1: (rare) of or occurring in summer; "the sky was a
           burnished aestival blue"; "estival winds" [syn:
           aestival, estival]