Plummet

n.
  1. A piece of lead attached to a line, used in sounding the depth of water.
  2. A plumb bob or a plumb line. See under Plumb, n.
  3. Hence, any weight.
  4. A piece of lead formerly used by school children to rule paper for writing.
    5. Plummet line ,
    a line with a plummet; a sounding line.