Once upon a time, there was a place where rain had not fallen for one whole year. The people had noticed that the rain would fall regularly at a specific time in a year, the months of July to August. They observed for the next few years. The same schedule was being followed. And thus, the smart people came to understand about the routine of the rain and then they named the period of rain, the rainy season.
This is an imaginary story so please don't say that it's all true. Hope I helped:)))