bridgeboard

详细解释:n. 木楼梯之侧板

详细解释：

bridge.board

n.（名词）
A notched board at either side of a staircase that supports the treads and risers.
木楼梯侧板，木楼梯小梁：在阶梯两边支撑楼梯的踏板和竖板的有凹口的木板