Plummet

Part of speech: noun (n.)

1. A piece of lead attached to a line, used in sounding the depth of water. I'll sink him deeper than e'er plummet sounded. Shak.

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. Plummet line, a line with a plummet; a sounding line.