kaftan vs nightgown

kaftan

noun
  • A long dress or shirt similar in style to those worn in the Eastern Mediterranean. 

  • A long tunic worn in the Eastern Mediterranean. 

nightgown

noun
  • A dressing gown. 

  • A long loose robe worn mainly by women for sleeping in. 

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