plumb-rule
(ˈplʌmruːl)
[f. plumb n. + rule n.]
An instrument used by builders, masons, carpenters, etc., for ensuring or testing the verticality of an erection; consisting of a plummet and line attached to and swinging freely on the surface of a narrow straight-edged board, marked with a longitudinal line which, when its position is vertical, coincides with the string.
| c 1391 Chaucer Astrol. ii. §38 Set thy pyn by a plom⁓rewle euene vpryht. 1578 Cooper Thesaurus, Ad perpendiculum, to trie by the plumbe rule. 1663 Gerbier Counsel 27 Brick-layers..to use often their line, and plum-rule. 1879 Cassell's Techn. Educ. iii. 140/2 note, A plumb-rule is a straight piece of wood, to which is attached a string with a plummet or lump of lead. |