fluctuation vs tremble

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. 

tremble

noun
  • A shake, quiver, or vibration. 

verb
  • To shake, quiver, or vibrate. 

  • To fear; to be afraid. 

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