Emily Dickinson Lexicon

AP-LUS'TER, or AP-LUS'TRE, n. [L. from Gr. αφλαιον, the summit of the poop of a ship.]

An ensign, or ornament carried by ancient ships. It was shaped like a plume of feathers, fastened on the neck of a goose or swan, and to this was attached a party-colored ribin, to indicate the course of the wind. – Addison. Encyc.