break-off vs head off

break-off

verb
  • To play the first shot in a game of snooker 

noun
  • That which breaks off, or is broken off 

  • A break, discontinuance, or interruption 

  • The first shot in a game of snooker or other cue-game 

head off

verb
  • To start out. 

  • To intercept. 

  • To avoid the undesirable consequences of; prevent. 

  • To turn away from the wind. 

  • To begin moving away. 

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