combat vs duke it out

combat

verb
  • To fight; to struggle against. 

  • To fight (with); to struggle for victory (against). 

noun
  • A battle, a fight (often one in which weapons are used). 

  • a struggle for victory 

duke it out

verb
  • To fight, especially with the fists. 

  • To argue heavily or at length. 

How often have the words combat and duke it out occurred in a corpus of books? (source: Google Ngram Viewer )