fluctuation vs uncertainty

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. 

uncertainty

noun
  • Something uncertain or ambiguous. 

  • Doubt; the condition of being uncertain or without conviction. 

  • A parameter that measures the dispersion of a range of measured values. 

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