A plateau is flat land that sits up high, reached by a climb; a plain is flat land that lies at low elevation, with no climb involved. Picture a tabletop (plateau) versus a tabletop laid flat on the ground (plain).
The core difference
A plateau is elevated flat land, while a plain is flat land at or near sea level.
- plateau — a large area of relatively flat, elevated land: the road climbs steeply before opening onto a wide plateau.
- plain — a large area of flat land, usually low-lying: herds of bison once roamed the great plains.
How to tell them apart
Both words describe flat, open terrain, but altitude is the giveaway. A plateau sits above the surrounding land, so you generally climb to reach one. A plain lies at or near the level of the land around it, so you simply walk or drive straight onto it.
Both words also drift into figurative use, and it is worth keeping those senses separate too. Plateau can describe progress that has levelled off, as in weight loss hitting a plateau, or it can be used as a verb: sales plateaued. Plain more often shows up as an adjective meaning simple or undecorated, as in a plain white dress, or clear and obvious, as in it was plain she disagreed.
