foe vs guardian angel

foe

noun
  • An enemy. 

  • A unit of energy equal to 10⁴⁴ joules. 

guardian angel

noun
  • A person who watches over another. 

  • A tutelary angel watching over a particular person in monotheistic contexts. 

How often have the words foe and guardian angel occurred in a corpus of books? (source: Google Ngram Viewer )