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plumb rule

American  

noun

  1. a device for determining perpendicularity, consisting of a narrow board with a plumb line and bob suspended from an upper edge.

plumb rule British  

noun

  1. a plumb line attached to a narrow board, used by builders, surveyors, etc

"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Etymology

Origin of plumb rule

1350–1400; Middle English plomreule

Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.