that is vs though

that is

adv

  • In other words; that is to say. Used to introduce a clarification or explanation 

though

adv

  • Used to intensify statements or questions; indeed. 

  • Despite that; however. 

conj

  • Despite the fact that; although. 

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