pla·teau / plaˈtō/ • n. (pl. -teaus or -teaux / -ˈtōz/ ) an area of relatively level high ground. ∎ fig. a state of little or no change following a period of activity or progress: the peace process had reached a plateau. ∎  [as adj.] denoting a group of American Indian peoples of the plateau country of western Canada and the U.S., including the Nez Percé.• v. (-teaus, -teaued, -teau·ing) [intr.] reach a state of little or no change after a time of activity or progress: the industry's problems have plateaued out.

plateau XVIII. — F. plateau, OF. platel, f. plat; see prec., -EL2.