swallowtail

Short definition from Wiktionary

Noun

1. 1
   The forked tail of a swallow.
2. 2
   Anything, such as a burgee, of a similar forked shape.
3. 3
   A type of tailcoat with two long tapering tails.
4. 4
   Any of various butterflies of the family Papilionidae, many of which have a long extension to each hindwing.