/ ˈplætəʊ; NAmE plæˈtoʊ/ noun , verb
■ noun ( pl. plat·eaux or plat·eaus / -təʊz; NAmE -ˈtoʊz/)
1.
an area of flat land that is higher than the land around it
2.
a time of little or no change after a period of growth or progress :
Inflation has reached a plateau.
■ verb
[ v ] plateau (out) to stay at a steady level after a period of growth or progress :
Unemployment has at last plateaued out.
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WORD ORIGIN
late 18th cent.: from French , from Old French platel , diminutive of plat level.