Monsoon

A monsoon is the name of a periodic wind, especially in the Indian Ocean and southern Asia. The word is also used to label the season in which this wind blows southwest in India and adjacent areas that is characterized by very heavy rainfall, and specifically the rainfall that is associated with this wind.

The word "monsoon" appears to have originated from the Arabic word mausim, which means season. It is most often applied to the seasonal reversals of the wind direction along the shores of the Indian Ocean, especially in the Arabian Sea, that blow from the southwest during one half of the year and from the northeast during the other. As monsoons have come to be better understood, the definition has been broadened to include almost all of the phenomena associated with the annual weather cycle within the tropical and subtropical continents of Asia, Australia, and Africa and the adjacent seas and oceans. It is within these regions that the most vigorous and dramatic cycles of weather events on Earth takes place.

(from the Goddard Space Flight Center's public domain Distributed Active Archive Center)