mention vs touch upon

mention

noun
  • A speaking or notice of anything, usually in a brief or cursory manner. Used especially in the phrase make mention of. 

  • A social media feed, a list of replies or posts mentioning a person. 

verb
  • To make a short reference to something. 

  • To utter a word or expression in order to refer to the expression itself, as opposed to its usual referent. 

touch upon

How often have the words mention and touch upon occurred in a corpus of books? (source: Google Ngram Viewer )