despair vs unhappiness

despair

noun
  • That which causes despair. 

  • Loss of hope; utter hopelessness; complete despondency. 

  • That which is despaired of. 

verb
  • To be hopeless; to have no hope; to give up all hope or expectation. 

  • To cause to despair. 

unhappiness

noun
  • The feeling of not being happy 

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