plumb line

American  

noun

1. a cord with a lead bob attached to one end, used to determine perpendicularity, the depth of water, etc.

2. plumb rule.

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plumb line British  

noun

1. a string with a metal weight at one end that, when suspended, points directly towards the earth's centre of gravity and so is used to determine verticality, the depth of water, etc

2. another name for plumb rule

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plumb line Scientific  

/ plŭm /

1. A line regarded as directed exactly toward the Earth's center of gravity.

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Etymology

Origin of plumb line

First recorded in 1530–40

Example Sentences

My father’s simple existence has been like a horizontal plumb line for me, one to gauge myself against.

From The Wall Street Journal • Jun. 14, 2018

Its southern latitude disguises just how far west the shipping channel reaches — far enough to catch a plumb line dropped from Cleveland.

From New York Times • May 18, 2018

He rolled up his sleeves, wiped the blade against the sole of his shoe, then hunkered down and closed one eye, like a carpenter with a plumb line.

From The New Yorker • Nov. 19, 2012

I had a beautiful Vidal-style pageboy, plumb line straight.

From BBC • May 24, 2012

Thus the next several days were to be spent using a plumb line and a measuring stick to obtain the relative positions of all atoms in a single nucleotide.

From "Double Helix" by James D. Watson