head-on vs man-to-man

head-on

adj
  • Direct, abrupt, blunt or unequivocal; not prevaricating. 

  • Of a collision, from the front or in the direction of motion. 

adv
  • With the front of a vehicle. 

  • With direct confrontation. 

noun
  • A collision from the front. 

man-to-man

adj
  • direct, forthright, and honest 

  • one-on-one 

adv
  • directly, forthrightly, and honestly 

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