The Collaborative International Dictionary of English v.0.48:

Etesian \E*te"sian\, a. [L. etesiae, pl., periodic winds, Gr. ?,
   fr. ? year: cf. F. ['e]t['e]sien.]
   Periodical; annual; -- applied to winds which annually blow
   from the north over the Mediterranean, esp. the eastern part,
   for an irregular period during July and August.
   [1913 Webster]