erratic vs fluctuant

erratic

adj
  • Unsteady, random; prone to unexpected changes; not consistent. 

  • Deviating from normal opinions or actions; eccentric; odd. 

noun
  • A rock moved from one location to another, usually by a glacier. 

  • Anything that has erratic characteristics. 

fluctuant

adj
  • That fluctuates or causes fluctuation. 

  • Used to describe a fluid-filled structure, such as an abscess, that produces a wave-like motion when palpated. 

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