fluctuation vs source

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. 

source

verb
  • To obtain or procure: used especially of a business resource. 

  • To find information about (a quotation)'s source (from which it comes): to find a citation for. 

noun
  • A reporter's informant. 

  • Source code. 

  • The name of one terminal of a field effect transistor (FET). 

  • Spring; fountainhead; wellhead; any collection of water on or under the surface of the ground in which a stream originates. 

  • The person, place, or thing from which something (information, goods, etc.) comes or is acquired. 

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