plumb line
柯林斯词典
1. N-COUNT A plumb line is a piece of string with a weight attached to the end that is used to check that something such as a wall is vertical or that it slopes at the correct angle. 铅垂线
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1. N-COUNT A plumb line is a piece of string with a weight attached to the end that is used to check that something such as a wall is vertical or that it slopes at the correct angle. 铅垂线