morning coat vs swallowtail

morning coat

noun
  • A man's formal coat worn as the principal item in morning dress, it also used for royal ascot and weddings. 

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 coat and swallowtail occurred in a corpus of books? (source: Google Ngram Viewer )