'Swallowtail' definitions:

Definition of 'swallowtail'

noun

A man's full-dress jacket with two long tapering tails at the back [syn: swallow-tailed coat, swallowtail, morning coat]

From: GCIDE

Swallowtail \Swal"low*tail`\, n.
1. (Carp.) A kind of tenon or tongue used in making joints. See Dovetail. [1913 Webster]
2. (Bot.) A species of willow. [1913 Webster]
3. (Fort.) An outwork with converging sides, its head or front forming a reentrant angle; -- so called from its form. Called also priestcap. [1913 Webster]
4. A swallow-tailed coat. [1913 Webster]
This Stultz coat, a blue swallowtail, with yellow buttons. --Thackeray. [1913 Webster]
5. An arrow. --Sir W. Scott. [1913 Webster]
6. (Zool.) 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. [1913 Webster]
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. [1913 Webster]

From: GCIDE

Priestcap \Priest"cap`\, n. (Fort.) A form of redan, so named from its shape; -- called also swallowtail. [1913 Webster]