contrast vs unknown quantity

contrast

noun
  • A difference between two objects, people or concepts. 

  • Something that is opposite of or strikingly different from something else. 

  • A control on a television, etc, that adjusts the amount of contrast in the images being displayed. 

  • Antithesis. 

  • is a substance used to increase the contrast of structures or fluids within the body in medical imaging. 

  • The degree of this difference. 

verb
  • To form a contrast. 

  • To set in opposition in order to show the difference or differences between. 

unknown quantity

noun
  • A person or thing whose nature or value is a mystery. 

  • Used other than figuratively or idiomatically: see unknown, quantity. 

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