cautioning vs heads-up

cautioning

noun
  • The act of giving a warning. 

heads-up

noun
  • A warning or call to pay attention; an advisory notice; a notice of what is to happen; a holler. 

  • Involving two players. (usually said when there are only two players in the table; or, when all players except two folded) 

adj
  • With head directly above the neck, eyes front. 

  • Alert; vigilant 

How often have the words cautioning and heads-up occurred in a corpus of books? (source: Google Ngram Viewer )