DICT.TW Dictionary Taiwan

 pos·tern /ˈpostɚ/
 後門,便門,旁門(a.)後面的,後門的,便門的,次等的

 Pos·tern n.
 1. Originally, a back door or gate; a private entrance; hence, any small door or gate.
    He by a privy postern took his flight.   --Spenser.
    Out at the postern, by the abbey wall.   --Shak.
 2. Fort. A subterraneous passage communicating between the parade and the main ditch, or between the ditches and the interior of the outworks.

 Pos·tern, a. Back; being behind; private. “The postern door.”
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 postern
      n : a small gate in the rear of a fort or castle