black tea vs tisane

black tea

noun
  • A cup of tea served without milk. 

  • Tea leaves which have been "fermented" (actually, oxidized) before drying to enhance their flavour (cf. green tea). 

tisane

noun
  • A medicinal drink, originally made from barley soaked in water. 

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