break-off vs knock

break-off

noun
  • A break, discontinuance, or interruption 

  • That which breaks off, or is broken off 

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

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

knock

noun
  • A blow or setback. 

  • An abrupt rapping sound, as from an impact of a hard object against wood. 

  • A sharp impact. 

  • A batsman's innings. 

  • Preignition, a type of abnormal combustion occurring in spark ignition engines caused by self-ignition; also, the characteristic knocking sound associated with it. 

  • Synonym of hunger knock 

  • A criticism. 

verb
  • To criticize verbally; to denigrate; to undervalue. 

  • To kick a ball towards another player; to pass. 

  • To rap one's knuckles against something, especially wood. 

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