plumb—¹n. A small mass or weight of lead, or any other heavy material (commonly brass), attached to a line and used by surveyors and engineers to indicate a vertical direction; a plummet; a plumb bob. ² adv Conforming to the direction of a line attached to a plumb; vertical; as, the wall is plumb. ³ v. to adjust or test by a plumb line; to cause to be perpendicular.

plumb bob—A conical device, usually of brass and suspended by a cord, by means of which a point can be projected vertically into space over relatively short distances.

plumb line—See line, plumb.

plumb line deflection—See deflection of the plumb line.

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Source: NSPS “Definitions of Surveying and Related Terms“, used with permission.

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