nightdress vs pyjamas

nightdress

noun
  • A nightgown; female attire designed to be worn to bed. 

pyjamas

noun
  • Britain standard spelling of pajamas (clothes for sleeping in). 

  • Britain standard spelling of pajamas (loose trousers worn by men and women in South Asia). 

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