/
ˈplatəʊ/
n.
 (pl. plateaux  
/-təʊz/
 or plateaus)
  - an area of fairly level high ground.
 - a state or period of little or no change following a period of activity or progress.
 
v.
 (plateaus, plateauing, plateaued)
 reach a state of little or no change.
Etymology
C18: from Fr., from OFr. platel, dimin. of plat ‘level’.