Plumb n.  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.


 plumb rule
      n : a plumb line attached to a narrow board