[from the Persian monsum, season]. The periodical winds in certain latitudes of India and the Indian Ocean. They continue five or six months from one direction, and then alter their course, and blow (after the tempestuous tumult of their shifting has subsided) during an equal space of time from an opposite point of the compass, with the same uniformity. They are caused by the unequal heating of land and water, and occur in the tropics, where the "trade" would constantly blow if it were not for the presence of land. (See winds.) The south-west monsoon is called by the Arabs khumseen, denoting fifty, as they suppose it to precede the overflowing of the Nile by fifty days. (See kamsin.)