put to death vs string up

put to death

verb
  • To kill as punishment for capital crimes; to execute. 

string up

verb
  • To kill (a person) by hanging, especially to lynch. 

  • To concatenate; to link in a line. 

  • To suspend by means of rope, cord or similar material. 

How often have the words put to death and string up occurred in a corpus of books? (source: Google Ngram Viewer )