The Collaborative International Dictionary
Plumb \Plumb\ (pl[u^]m), n. [F. plomb, L. plumbum lead, a leaden ball or bullet; cf. Gr. mo`lybos, mo`libos, mo`lybdos. Cf. Plummet, Plunge.] 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. Plumb bob. See Bob, 4. Plumb joint, in sheet-metal work, a lap joint, fastened by solder. Plumb level. See under Level. Plumb line.
The cord by which a plumb bob is suspended; a plummet.
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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.
Wiktionary
alt. A metal weight attached to the end of a plumb line. n. A metal weight attached to the end of a plumb line.
WordNet
Wikipedia
A plumb bob or a plummet is a weight, usually with a pointed tip on the bottom, that is suspended from a string and used as a vertical reference line, or plumb-line. It is essentially the vertical equivalent of a " water level".
The instrument has been used since at least the time of ancient Egypt to ensure that constructions are "plumb", or vertical. It is also used in surveying to establish the nadir with respect to gravity of a point in space. They are used with a variety of instruments (including levels, theodolites, and steel tapes) to set the instrument exactly over a fixed survey marker, or to transcribe positions onto the ground for placing a marker.
Usage examples of "plumb bob".
Which is where the plumb bob and the laser distance meter come in.
As Kaitlyn watched, the plumb bob began to swing in circles over a section of the map.
I sat stunned, as if spellbound by a sorcerer, unable to move, unable even to blink, my heart hanging like an iron plumb bob in my chest, numb to emotion, unable to feel the pistol in my hand, unable to see anything whatsoever, not even the dead man whom I knew to be at the other end of the car seat, briefly blinded by shock, baffled and bound by blackness, temporarily deafened either by the gunfire or perhaps by a desperate desire not to hear even the inner voice of my conscience chattering about consequences.
The weight of the heavy hook at the end worked like a plumb bob to keep the cable from blowing back into the tail rotor.
The dangling piton acted like a plumb bob which allowed him to check whether his line of sight—.
Malachi ceremonially destroyed his T-square and plumb bob before beginning construction.