To bypass obstacles covertly by drilling a hole and climbing over a wall; figuratively, to engage in a clandestine affair or to burglarize a house.
夜深人静时，小偷钻穴逾墙，潜入无人居住的别墅
In the dead of night, the thief broke in by drilling a hole and climbing over a wall, sneaking into the unoccupied villa.
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