fluctuation vs modification

fluctuation

noun
  • A wavering; unsteadiness. 

  • In medicine, a wave-like motion or undulation of a fluid in a natural or abnormal cavity (e.g. pus in an abscess), which is felt during palpation or percussion. 

  • A motion like that of waves; a moving in this and that direction. 

modification

noun
  • A change to an organism as a result of its environment that is not transmissable to offspring. 

  • the change undergone by a word when used in a construction (for instance am => 'm in I'm) 

  • The act of making a change to something while keeping its essential character intact; an alteration or adjustment. 

  • a change to a word when it is borrowed by another language 

  • The result of modifying something; a new or changed form. 

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