from
The Collaborative International Dictionary of English v.0.48
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.
[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.
[1913 Webster]