wWhisker 是指一根胡须，by a whisker, 就是指：就差那么一点点；差一点。

【例句】
You escaped serious injury by a whisker, so consider yourselves very lucky.
你差一点就受重伤, 你应该觉得自己很幸运.

He and his son-in-law won the Olympic trials by a whisker.
他跟自己的女婿一队，在奥运选拔赛中险胜。