IPA: /ˈpleɪnz.mən/
KK: /ˈpleɪnzˌmæn/
A person who lives in or comes from the flat, open areas of land, especially in the prairie regions of the United States.
The plainsman rode across the vast fields, enjoying the beauty of the open landscape.
Plainsman → It is formed from "plain" (from Old French *plain*, meaning flat or level) and "-sman" (meaning a person who). A plainsman is a person who lives on or is associated with flat, level land.
Think of someone who lives on 'flat land' ('plain') — the '-sman' just means a person. A plainsman is someone who is connected to the plains.