head-to-head vs parley

head-to-head

adv

  • Directly, one-to-one. 

  • Facing one another. 

adj

  • Direct, one-to-one. 

parley

verb

  • To have a discussion, especially one between enemies. 

noun

  • A conference, especially one between enemies. 

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