slag off vs vilify

slag off

verb
  • To talk insultingly to or about someone or something; usually one who is not present. 

  • To purify by melting and removing slag. 

vilify

verb
  • To say defamatory things about someone or something; to speak ill of. 

  • To belittle through speech; to put down. 

How often have the words slag off and vilify occurred in a corpus of books? (source: Google Ngram Viewer )