—n. 1. a land area having a relatively level surface considerably raised above adjoining land on at least one side, and often cut by deep canyons.
2. a period or state of little or no growth or decline: to reach a plateau in one's career. 3. Psychol.a period of little or no apparent progress in an individual's learning, marked by an inability to increase speed, reduce number of errors, etc., and indicated by a horizontal stretch in a learning curve or graph.
4. a flat stand, as for a centerpiece, sometimes extending the full length of a table.
—v.i. to reach a state or level of little or no growth or decline, esp. to stop increasing or progressing; remain at a stable level of achievement; level off: After a period of uninterrupted growth, sales began to plateau.
—v.t. to cause to remain at a stable level, esp. to prevent from rising or progressing: Rising inflation plateaued sales income.