cop out vs shirk

cop out

verb
  • To avoid or shirk, either by failing to perform, or by performing in a grossly insufficient, negligent, or superficial manner. 

  • To plead guilty and ask for mercy. 

shirk

verb
  • To evade an obligation; to avoid the performance of duty, as by running away. 

  • To avoid, especially a duty, responsibility, etc.; to stay away from. 

  • To procure by petty fraud and trickery; to obtain by mean solicitation. 

noun
  • One who shirks, who avoids a duty or responsibility. 

  • The unforgivable sin of idolatry. 

How often have the words cop out and shirk occurred in a corpus of books? (source: Google Ngram Viewer )