the cover of darkness; to do something illicit under the cover of a diversion
Definitions (粵典–words.hk)
語句
全句「明修棧道，暗度陳倉」。楚漢時期，韓信出兵攻打項羽，表面上公開派人修築棧道，暗中就由陳倉出兵，最後平定三秦。後來比喻出其不意嘅戰略、又或者暗中進行嘅活動。 to operate covertly, especially when making an advance in a broad sense; literally, (to pretend to repair the gallery roads on one side while) having the troops secretly pass through Chencang, or to feign an advancement on one side while actually advancing through the other