ennui vs variability

ennui

verb
  • To make bored or listless; to weary. 

noun
  • A gripping listlessness or melancholia caused by boredom; depression. 

variability

noun
  • The state or characteristic of being variable. 

  • The degree to which a thing is variable. In data or statistics this is often a measurement of distance from the mean or a description of data range. 

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