evening dress vs nightdress

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. 

nightdress

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

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