gallows tree vs hangman

gallows tree

noun
  • A tree used as a gallows, a tree from which people are hung (killed by hanging). 

hangman

noun
  • An executioner responsible for hanging criminals. 

  • Someone responsible for hanging pictures and other artworks in a gallery, museum etc. 

  • A guessing game where one has to guess the word an opponent is thinking of by guessing one letter at a time, and involving the gradual drawing of a stick figure hanging from the gallows. 

How often have the words gallows tree and hangman occurred in a corpus of books? (source: Google Ngram Viewer )