allusion vs tropology

allusion

noun
  • An indirect reference; a hint; a reference to something supposed to be known, but not explicitly mentioned 

tropology

noun
  • A recurring motif or metaphor, a trope; an interplay of tropes. 

  • The use of a trope (metaphor or figure of speech). 

  • The interpretation of scripture or other work in order to educe moral or figurative meaning; a treatise of such interpretation. 

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