nightrobe vs pajamas

nightrobe

noun
  • A robe to be worn at night; a nightgown. 

pajamas

noun
  • Clothes for wearing to bed and sleeping in, usually consisting of a loose-fitting shirt and pants/trousers. 

  • Loose-fitting trousers worn by both sexes in various southern Asian countries including India. 

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