evening dress vs nightgown

evening dress

noun
  • An elegant dress worn by women, especially for social events in the evening, an evening gown. 

  • formal attire worn for evening social events. 

nightgown

noun
  • A dressing gown. 

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

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