halfhearted vs tepid

halfhearted

adj
  • Lacking full energy, effort, commitment, or resolve. 

tepid

adj
  • Uninterested; exhibiting little passion or eagerness; lukewarm. 

  • Lukewarm; neither warm nor cool. 

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