in-joke vs metaphor

in-joke

noun
  • Synonym of inside joke (“a joke that is understood or meant to be understood only by certain people who are aware of the details”) 

metaphor

noun
  • The use of a word or phrase to refer to something other than its literal meaning, invoking an implicit similarity between the thing described and what is denoted by the word or phrase. 

  • A word or phrase used in such implied comparison. 

  • The use of an everyday object or concept to represent an underlying facet of the computer and thus aid users in performing tasks. 

verb
  • To use a metaphor. 

  • To describe by means of a metaphor. 

How often have the words in-joke and metaphor occurred in a corpus of books? (source: Google Ngram Viewer )