Definition of swallowtail
noun
1 (also swallowtail butterfly) a large brightly coloured butterfly with tail-like projections on the hindwings. - Family Papilionidae: many species, including the European Papilio machaon, of fenland country
2 [usually as modifier] a deeply forked tail. a thing resembling a deeply forked tail in shape:a black swallowtail coat
