impending vs on the boil

impending

noun
  • Something that impends or threatens; an expected event. 

adj
  • Approaching; drawing near; about to happen or expected to happen. 

on the boil

prep
  • About to happen; imminent. 

  • Playing exceptionally well. 

  • Going smoothly; working well. 

  • continuing; active; in a state of activity or development. 

  • simmering strongly and about to boil. 

  • boiling. 

  • (Of a player taking a pass) running at full speed towards the opposition. 

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