false friend vs informer

false friend

noun
  • Used other than figuratively or idiomatically: see false, friend. 

  • A word in a language that bears a deceptive resemblance to a word in another language but in fact has a different meaning. 

informer

noun
  • One who informs someone else about something. 

  • One who informs, animates, or inspires. 

  • A person who tells authorities about improper or illegal activity. 

How often have the words false friend and informer occurred in a corpus of books? (source: Google Ngram Viewer )