Definition of plumb line noun from the Oxford Advanced Learner's Dictionary


plumb line

BrE BrE//ˈplʌm laɪn//
; NAmE NAmE//ˈplʌm laɪn//
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a piece of thick string with a weight attached to one end, used to find the depth of water or to test whether a wall, etc. is straight
See the Oxford Advanced American Dictionary entry: plumb line