herbal tea vs infusion

herbal tea

noun
  • A beverage made by infusing the leaves of various herbs, generally not including true tea (Camellia sinensis). 

infusion

noun
  • A product consisting of a liquid which has had other ingredients steeped in it to extract useful qualities. 

  • The administration of liquid substances directly into a vein for medical purposes; perfusion. 

  • The act of steeping or soaking a substance in liquid so as to extract medicinal or herbal qualities. 

  • The act of installing a quality into a person. 

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