English speakers picked up the word monsoon (describing a period of rainy tropical winds) from Dutch speakers (who said monssoen), who picked it up from Portuguese speakers (who said moncao), who picked it up from Arab traders. These Arabic-speaking merchants used mawsim as a word for "seasons", since the monsoons marked the seasons pretty well. Since they marked the seasons, it then makes sense that the etymology would proceed back to the Arabic word for "mark", wasama. This is said to have origins in the root w-s-m, which if true probably means that it ultimately goes back to Proto-Semitic and the theorized Proto-Afroasiatic tongue. If this is not the case, the word may have origins in one of the Indian languages, but nothing is for sure. Surprisingly, usage is significantly higher for the word monsoon in Great Britain than in America.
Adam Aleksic, a leading contender for valedictorian of his high school, is a 211-month-old boy with disturbing interests in etymology, vexillology, geography, and law. Adam would like to one day visit Tajikistan and probably isn't spying for the Kyrgyz government.
The Etymology Nerd