plateau vs quiescent period

plateau

verb
  • (of a varying quantity) To reach a stable level after a period of increase; to level off. 

noun
  • A comparatively stable level after a period of increase. 

  • A notable level of attainment or achievement. 

  • A largely level expanse of land at a high elevation; tableland. 

quiescent period

How often have the words plateau and quiescent period occurred in a corpus of books? (source: Google Ngram Viewer )