fluctuation vs strength

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. 

strength

noun
  • The intensity of a force or power; potency. 

  • The quality or degree of being strong. 

  • The strongest part of something; that on which confidence or reliance is based. 

  • A positive attribute. 

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