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 p...