bed·post /-ˌpost/
  床柱
  Bed·post n.
  1. One of the four standards that support a bedstead or the canopy over a bedstead.
  2. Anciently, a post or pin on each side of the bed to keep the clothes from falling off.  See Bedstaff.
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  bedpost
       n : any of 4 vertical supports at the corners of a bedstead