flak vs hit piece

flak

noun
  • Adverse criticism. 

  • A public-relations spokesperson. 

  • Anti-aircraft shell fire. 

  • Ground-based anti-aircraft guns firing explosive shells. 

hit piece

noun
  • A published article or post aiming to sway public opinion by presenting false or biased information in a way that appears objective and truthful. 

How often have the words flak and hit piece occurred in a corpus of books? (source: Google Ngram Viewer )