give a warning to vs tip off

give a warning to

tip off

verb
  • To begin. 

  • To alert or inform (someone), especially confidentially. 

  • To use a particular brush technique for producing a flawless surface on a wet coat of paint. 

  • To put the ball in play by throwing it up between two opponents. 

How often have the words give a warning to and tip off occurred in a corpus of books? (source: Google Ngram Viewer )