rapids vs waterfall

rapids

waterfall

verb
  • To drink (something) from a container by pouring it from a height so as not to touch one's lips to the rim. 

  • To fall like a waterfall. 

  • Synonym of recycle 

noun
  • A waterfall-like outpouring of liquid, smoke, etc. 

  • A flow of water over the edge of a cliff. 

  • Waterfall model 

  • The action of drinking from a vessel without touching it with the lips, considered more sanitary for a shared vessel. 

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