swallowtail vs tailcoat

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. 

tailcoat

noun
  • Any coat with similar tails. 

  • A formal evening jacket with an extended back panel; a dress coat. 

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