a type of large colourful butterfly

having a shape that is divided into two at one end, so that it has two points

The flag has a swallowtail shape. 旗帜呈燕尾状。

used to describe a jacket or coat that has two long pointed parts at the back

He wore a white bow tie and a swallowtail coat. 他打着白色领结，穿着燕尾服。