passion vs slow burn

passion

noun
  • An object of passionate or romantic love or strong romantic interest. 

  • Fervor, determination. 

  • A display, musical composition, or play meant to commemorate the suffering of Jesus. 

  • The suffering of Jesus leading up to and during his crucifixion. 

  • Any great, strong, powerful emotion, especially romantic love or extreme hate. 

  • A true desire sustained or prolonged. 

  • Sexual intercourse, especially when very emotional. 

verb
  • To give a passionate character to. 

slow burn

noun
  • A romantic story (especially a work of fan fiction) in which the central relationship develops slowly. 

  • A gradually increasing feeling of anger or frustration. 

adj
  • Developing slowly over the course of the story. 

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