fluctuate vs quaver

fluctuate

verb
  • To be irresolute; to waver. 

  • To cause to vary irregularly. 

  • To vary irregularly; to swing. 

  • To undulate. 

quaver

verb
  • To utter quaveringly. 

  • To shake in a trembling manner. 

  • To use the voice in a trembling manner, as in speaking or singing. 

noun
  • A trembling shake. 

  • an eighth note, drawn as a crotchet (quarter note) with a tail. 

  • A trembling of the voice, as in speaking or singing. 

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