plural of plain
"The vast plains stretch endlessly from the river valley to the distant mountains."
Third-person singular simple present indicative form of plain
"The sun glows brightly over the vast plains at dawn."
In plain English: To plains means to make something flat and level, usually by cutting down hills or removing obstacles so it looks smooth.
"She decided to plains her worries away by going for a long walk in the park."
The Great Plains region of North America.
"The cattle ranches spread across the vast grasslands of the Great Plains."