They had killed the remaining horse, but the monsoonal rains descended, and in the steamy atmosphere the meat turned putrid.
1580s, "trade wind of the Indian Ocean," from Dutch monssoen, from Portuguese monçao, from Arabic mawsim "time of year, appropriate season" (for a voyage, pilgrimage, etc.), from wasama "he marked." When it blows from the southwest (April through October) it brings heavy rain, hence "heavy episode of rainfall during the rainy season" (1747).
A wind system that affects large climatic regions and reverses direction seasonally.
Note: The Asiatic monsoon brings heavy rains to Southeast Asia in spring and summer.