swallowtail

swallow +‎ tail

• (UK) IPA^(key): /ˈswɒl.əʊˌteɪl/

swallowtail (plural swallowtails)

1. The forked tail of a swallow.
2. Anything, such as a burgee, of a similar forked shape.
3. A type of tailcoat with two long tapering tails.^Wp
   • 1906, Stanley J[ohn] Weyman, chapter I, in Chippinge Borough, New York, N.Y.: McClure, Phillips & Co., OCLC 580270828, page 01:

     It was April 22, 1831, and a young man was walking down Whitehall in the direction of Parliament Street. He wore shepherd's plaid trousers and the swallow-tail coat of the day, with a figured muslin cravat wound about his wide-spread collar.

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