duel vs head-to-head

duel

verb
  • To engage in a battle. 

noun
  • Arranged, regular combat between two private persons, often over a matter of honor. 

  • Historically, the wager of battle (judicial combat). 

  • Any battle or struggle between two contending persons, forces, groups, or ideas. 

head-to-head

adv
  • Directly, one-to-one. 

  • Facing one another. 

adj
  • Direct, one-to-one. 

How often have the words duel and head-to-head occurred in a corpus of books? (source: Google Ngram Viewer )