dress suit vs swallowtail

dress suit

noun
  • A type of formal attire for men, normally consisting of a jacket (traditionally with tails), trousers, waistcoat, shirt and tie (traditionally a bow tie). 

  • A type of formal attire for women, typically a jacket over a dress, or a jacket and blouse with trousers or a skirt. 

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