fluctuate vs overswell

fluctuate

verb
  • To cause to vary irregularly. 

  • To vary irregularly; to swing. 

  • To undulate. 

  • To be irresolute; to waver. 

overswell

verb
  • To cause (something) to be too swollen or large; to become too swollen or large. 

  • To swell or rise above (something, especially the rim of a container, the sides of something hollow, etc.). 

noun
  • An excessive or sudden increase or flood (of something). 

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