housecoat vs nightgown

housecoat

noun
  • A bathrobe or dressing gown. 

  • A longish dress-like garment of one piece, fastening down the front, worn about the house. 

nightgown

noun
  • A dressing gown. 

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

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