ETESIÆ, or Etesian winds, are such as blow at stated times of the year, from what part forever of the compass they come. They are so called from the Greek word ἑτοῖς, "year," being yearly or annenary winds, such as our seamen call monsoons and trade-winds, which in some parts of the world continue constantly blowing for certain stated seasons of the year. Thus, the north winds, which, during the dog-days, constantly blow upon the coasts of Egypt, and hinder all ships from sailing out of Alexandria for that season, are called etesiae in Caesar's Commentaries. In other authors, the west and east winds are called etesiae, when they continue blowing for certain seasons of the year.

Cellarius endeavours to prove that those winds are properly etesian which blow from that part of the horizon which is between the north and west about the time of the solstice. In ancient writers, they are represented as of a very mild and gentle nature; and were called by mariners somnificulæ and delicati, from their sleeping or ceasing to blow in the night.