What is "priestcap"

Swallowtail \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.

n. A form of redan in fortifications; a swallowtail.