A little mass or weight of lead, or the like, attached to a line, and used by builders, etc., to indicate a vertical direction; a plummet; a plumb bob. See Plumb line, below. [1913 Webster]

Plumb bob. See Bob, 4. -- Plumb joint, in sheet-metal work, a lap joint, fastened by solder. -- Plumb level. See under Level. -- Plumb line. (a) The cord by which a plumb bob is suspended; a plummet. (b) A line directed to the center of gravity of the earth. -- Plumb rule, a narrow board with a plumb line, used by builders and carpenters.

plumb, a.

Perpendicular; vertical; conforming the direction of a line attached to a plumb; as, the wall is plumb. [1913 Webster]

plumb, adv.

In a plumb direction; perpendicularly. Milton. [1913 Webster]

plumb, v. t.

To adjust by a plumb line; to cause to be perpendicular; as, to plumb a building or a wall. [1913 Webster]
To sound with a plumb or plummet, as the depth of water; hence, to examine by test; to ascertain the depth, quality, dimension, etc.; to sound; to fathom; to test. [1913 Webster]
"He did not attempt to plumb his intellect." [1913 Webster]
To seal with lead; as, to plumb a drainpipe. [1913 Webster]
To supply, as a building, with a system of plumbing. [1913 Webster]

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OXFORD DICTIONARY

plumb, n., adv., adj., & v.
--n. a ball of lead or other heavy material, esp. one attached to the end of a line for finding the depth of water or determining the vertical on an upright surface.
--adv.
1 exactly (plumb in the centre).
2 vertically.
3 US sl. quite, utterly (plumb crazy).
--adj.
1 vertical.
2 downright, sheer (plumb nonsense).
3 Cricket (of the wicket) level, true.
--v.tr.
1 a measure the depth of (water) with a plumb. b determine (a depth).
2 test (an upright surface) to determine the vertical.
3 reach or experience in extremes (plumb the depths of fear).
4 learn in detail the facts about (a matter).

Idiom

out of plumb not vertical. plumb-line a line with a plumb attached. plumb-rule a mason's plumb-line attached to a board.

plumb, v.
1 tr. provide (a building or room etc.) with plumbing.
2 tr. (often foll. by in) fit as part of a plumbing system.
3 intr. work as a plumber.

Etymology

back-form. f. PLUMBER

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THESAURUS

plumb

T square, absolute, absolutely, accurately, all-embracing, all-encompassing, all-out, all-pervading, answer, aplomb, appraise, appreciate, assay, assess, at right angles, azimuth circle, bang, bar, barricade, batten, batten down, bob, bolt, born, bottom, broad-based, button, button up, calculate, calibrate, caliper, cast the lead, check a parameter, choke, choke off, clap, clean, clear, clear up, close, close up, come alive, completely, comprehensive, compute, congenital, constrict, consummate, contain, contract, cover, crack, dead, debug, decipher, decode, deep-dyed, definitely, delve, delve into, descry, dial, dig into, directly, discern, disentangle, divide, divine, do, dope, dope out, downright, dyed-in-the-wool, egregious, entirely, estimate, evaluate, even, exactly, exhaustive, explain, explore, expressly, faithfully, fasten, fathom, figure out, find out, find the answer, find the solution, flush, fold, fold up, full, fully, gauge, get, get right, go into, graduate, guess, guess right, have it, hit it, in all respects, in every respect, indagate, intensive, interpret, investigate, ipsissimis verbis, irretrievably, irrevocably, just, kerplunk, key, latch, lead, literally, literatim, lock, lock out, lock up, look into, make a sounding, make out, measure, mensurate, mete, meter, normal, occlude, omnibus, omnipresent, open the lock, orthodiagonal, orthogonal, out-and-out, outright, pace, padlock, peer into, penetrate, perceive, perfect, perfectly, perpendicular, perpendicularly, pervasive, pierce, plain, plop, plumb bob, plumb line, plumb rule, plumb the depths, plumb-line, plummet, plump, plunging, plunk, point-blank, poke into, positively, precipitous, precisely, prize, probe, pry into, psych, psych out, pure, puzzle out, quantify, quantize, quite, radical, rate, ravel, ravel out, regular, resolve, riddle, right, right angle, right-angle, right-angled, right-angular, rigidly, rigorously, sandbag, seal, seal off, seal up, search into, secure, see, see daylight, see into, see the light, see through, set, set square, sheer, sheerly, shut, shut the door, shut up, sift, sinker, size, size up, slam, slap, sling the lead, smack, smack-dab, snap, solve, sort out, sound, span, spang, spot, square, squarely, squeeze shut, stark, steep, step, straight, straight-up, straight-up-and-down, strangle, strictly, survey, sweeping, take a reading, take soundings, thorough, thoroughgoing, thoroughly, through-and-through, to the letter, total, triangulate, try square, ubiquitous, unconditional, undeviatingly, undo, unerringly, universal, unlock, unmitigated, unqualified, unravel, unrelievedly, unreserved, unrestricted, unriddle, unscramble, untangle, untwist, unweave, up and down, up-and-down, upright, utter, utterly, valuate, value, verbally, verbatim, verbatim et litteratim, veritable, vertical, vertical circle, weigh, weight, wholesale, wholly, word by word, word for word, work, work out, zip up, zipper

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ROGET THESAURUS

plumb

Depth

VB be deep, render deep, deepen, plunge, sound, fathom, plumb, cast the lead, heave the lead, take soundings, make soundings, dig.

Verticality

N verticality, erectness, perpendicularity, right angle, normal, azimuth circle, wall, precipice, cliff, elevation, erection, square, plumb line, plummet, vertical, upright, erect, perpendicular, plumb, normal, straight, bolt, upright, rampant, standing up, rectangular, orthogonal, vertically, up, on end, up on end, right on end, a plomb, endwise, one one's legs, at right angles.

Closure

VB close, occlude, plug, block up, stop up, fill up, bung up, cork up, button up, stuff up, shut up, dam up, blockade, obstruct, bar, bolt, stop, seal, plumb, choke, throttle, ram down, dam, cram, trap, clinch, put to the door, shut the door.

Measurement

VB measure, mete, determine, assay, evaluate, value, assess, rate, appraise, estimate, form an estimate, set a value on, appreciate, standardize, span, pace step, apply the compass, gauge, plumb, probe, sound, fathom, heave the log, heave the lead, survey, weigh, take an average, graduate.

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