blacklist vs keep at arm's length

blacklist

verb
  • To place on a blacklist; to mark a person or entity as one to be shunned or banned. 

noun
  • A list or set of people or entities to be shunned or banned. 

keep at arm's length

verb
  • Avoid a close relationship. 

  • Avoid direct confrontation or struggle. 

  • Keep at a distance, away from one's body. 

How often have the words blacklist and keep at arm's length occurred in a corpus of books? (source: Google Ngram Viewer )