释义
n.
the door of a stable, divided into two parts horizontally allowing one half to be shut and the other left open
（上下两部分可以分别开关的）两截马厩门。
短语
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shut （或bolt ）the stable door after the horse has bolted try to avoid or prevent something bad or unwelcome when it is already too late to do so 亡羊补牢，为时晚矣