fervor vs zeal

fervor

noun
  • An intense, heated emotion; passion, ardor. 

  • Heat. 

  • A passionate enthusiasm for some cause. 

zeal

noun
  • The fervour or tireless devotion for a person, cause, or ideal and determination in its furtherance; diligent enthusiasm; powerful interest. 

  • The collective noun for a group of zebras. 

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