four-post·er /ˌforˈpostɚ/
  四柱大型臥床
  Four-post·er n. A large bedstead with tall posts at the corners to support a canopy or curtains. [Colloq.]
  ◄ ►
  four-poster
       n : a bed with posts at the four corners that can be used to
           support a canopy or curtains