\Swal"low*tail`\, n.
1. (Carp.) A kind of tenon or tongue used in making joints.
   See {Dovetail}.
2. (Bot.) A species of willow.
3. (Fort.) An outwork with converging sides, its head or
   front forming a re["e]ntrant angle; -- so called from its
   form. Called also {priestcap}.
4. A swallow-tailed coat.
         This Stultz coat, a blue swallowtail, with yellow
         buttons.                              --Thackeray.
5. An arrow. --Sir W. Scott.
6. (Zo["o]l.) Any one of numerous species of large and
   handsome butterflies, belonging to Papilio and allied
   genera, in which the posterior border of each hind wing is
   prolongated in the form of a long lobe.
Note: The black swallowtail, or asterias (see {Papilio}), the
      blue swallowtail, or philenor, the tiger swallowtail,
      or turnus (see {Turnus}), and the zebra swallowtail, or
      ajax (see under {Zebra}) are common American species.
      See also {Troilus}.