n. [ OF. posterne, posterle, F. poterne, fr. L. posterula, fr. posterus coming after. See Posterior. ] 1. Originally, a back door or gate; a private entrance; hence, any small door or gate. [ 1913 Webster ] He by a privy postern took his flight. Spenser. [ 1913 Webster ] Out at the postern, by the abbey wall. Shak. [ 1913 Webster ] 2. (Fort.) A subterraneous passage communicating between the parade and the main ditch, or between the ditches and the interior of the outworks. Mahan. [ 1913 Webster ] | 