fluctuation vs stiffness

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. 

stiffness

noun
  • inelegance; a lack of relaxedness. 

  • rigidity or a measure of rigidity. 

  • inflexibility or a measure of inflexibility. 

  • muscular tension due to unaccustomed or excessive exercise or work; soreness. 

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