IPA: //sʌbˈbeɪsɪn//
KK: /sʌbˈbeɪsɪn/
A smaller area of land that drains into a river or lake, which is part of a larger drainage area.
The subbasin collects rainwater and directs it to the main river.
Subbasin → It is formed from "sub-" (meaning under or below) and "basin" (from Old French *bacin*, meaning a receptacle or container). The word "subbasin" refers to a smaller basin that is located beneath or within a larger basin.
Think of something that is a 'container' ('basin') that is 'under' ('sub-') another container — that's what a subbasin is.