Monsoon  (mŏn-sōōn ´).—A wind blowing part of the year from one direction, alternating with a wind from the opposite direction—a term applied particularly to periodical winds of the Indian Ocean, which blow from the southwest from the latter part of May to the middle of September, and from the northeast from about the middle of October to the middle of December.
Monsoons and Their Location

The monsoons or periodical winds of the Indian Ocean owe their origin to the same cause which gives rise to the trade-winds, though they acquire a different character in consequence of the proximity of the land. In the southern portions of the ocean which are remote from this cause of disturbance, the trade-wind blows with its wonted regularity; but in the seas occupying the region between the eastern coast of Africa on the one side, and the Malay peninsula and the island of Sumatra on the other, the course of the trade-wind is reversed for half the year. This change occurs from April to October; the sun at that period being vertical north of the equator, and the land in the adjacent regions acquiring in consequence a high temperature, and the air over the sea being cooler than that over the land, a south-west wind prevails. This wind, called the “south-west monsoon,” commences at about three degrees south of the equator, and passing over the ocean arrives charged with moisture, and accordingly usually deposits copious supplies of rain in India and some of the adjoining territories. In the remaining half of the year, or from October to April, the wind assumes the ordinary north-easterly direction of the trade-wind.

Sea-breezes, which occur in regions bordering on the ocean in hot climates, are produced by causes similar to those which give rise to the south-west monsoon, but on a more limited scale of action, and changing their direction daily.