head-on vs serious

head-on

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

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

noun
  • A collision from the front. 

adv
  • With the front of a vehicle. 

  • With direct confrontation. 

serious

adj
  • Really intending what is said (or planned, etc); in earnest; not jocular or deceiving 

  • Committed. 

  • Without humor or expression of happiness; grave in manner or disposition 

  • Important; weighty; not insignificant 

adv
  • In a serious manner; seriously. 

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