swallowtail

hännystakki The forked tail of a swallow.
Anything, such as a burgee, of a similar forked shape.
A type of tailcoat with two long tapering tails.(w)
(RQ:SWymn ChpngBrgh)

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.