postern/ˈpɔstən; `pɑstɚn/ n(arch 古) side or back entrance, esp a concealed entrance to a castle, etc 边门; 後门; 边道; 便道; （尤指城堡等的）暗道 [attrib 作定语]a postern door/gate 後门.
牛津英汉双解词典