morning dress vs swallowtail

morning dress

noun
  • Clothing to be worn in the morning or daytime, as opposed to the evening; now (specifically), a man's formal suit consisting of a (usually) dark grey morning coat, waistcoat and striped trousers accompanied with a top hat, white shirt and tie or cravat. 

  • A woman's dress designed for informal day wear. 

swallowtail

noun
  • A type of tailcoat with two long tapering tails.ᵂᵖ 

  • The forked tail of a swallow. 

  • Anything, such as a burgee, of a similar forked shape. 

  • Any of various butterflies of the family Papilionidae, many of which have a long extension to each hindwing. 

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