plumb line

plumb line
    n 1: a cord from which a metal weight is suspended pointing
         directly to the earth's center of gravity; used to
         determine the vertical from a given point [syn: {plumb
         line}, {perpendicular}]
    

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]