Brewer's: Etesian Wind
(An). “Etesia Flabra Aquilorium, ” says Lucretius (v. 741). A wind which rises annually about the dog-days, and blows forty days together in the same direction. It is a gentle and mild wind. (Greek, annual.)
Deem not, good Porteus, that in this my song I mean to harrow up thy humble mind, And stay that voice in London known so long; For balm and softness, an Etesian wind.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894