E. Cobham Brewer 1810–1897. Dictionary of Phrase and Fable. 1898.
Trade Winds.
Winds that trade or tread in one uniform track. In the northern hemisphere they blow from the north-east, and in the southern hemisphere from the south-east, about thirty degrees each side of the equator. In some places they blow six months in one direction, and six in the opposite. It is a mistake to derive the word from trade (commerce), under the notion that they are “good for trade.” (Anglo-Saxon, tredde-wind, a treading wind—i.e. wind of a specific “beat” or tread; tredan, to tread.)
