Source : Webster's Revised Unabridged Dictionary (1913)

Plumb \Plumb\, n. [F. plomb, L. plumbum lead, a leaden ball or
   bullet; cf. Gr. ?, ?, ?. 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}.
   (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.

Source : WordNet®

plumb bob
     n : the metal bob of a plumb line [syn: {plumb}, {plummet}]