though vs unless

though

conj
  • Despite the fact that; although. 

adv
  • Used to intensify statements or questions; indeed. 

  • Despite that; however. 

unless

conj
  • If not; used with counterfactual conditionals. 

  • Except if; used with hypothetical conditionals. 

  • Except on a specified condition; if not. 

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