Definition from Wiktionary, the free dictionary
four-poster (not comparable)
- (of a bed) Having four vertical columns, one in each corner, that support a tester, so that curtains can be hung to exclude draughts from the sleeper.
Used only attributively.
four-poster (plural four-posters)
- A four-poster bed, which has four high posts, one at each corner, supporting a canopy.