Adjective

1. truly vertical
2. Describing an LBW where the batsman is hit on the pads directly in front on his wicket and should be given out.

Adverb

1. In a vertical direction.
2. Squarely, directly; completely.

   It hit him plumb in the middle of his face.

   Years ago the well plumb dried out, not a drop of water in there since.

Noun

1. A little mass of lead, or the like, attached to a line, and used by builders, etc., to indicate a vertical direction; a plummet; a plumb bob (UK); a plumb line (US).
2. A weight on the end of a long line, used by sailors to determine the depth of water.

Verb

1. To determine the depth, generally of a liquid; to sound.
2. To attach to a water supply and drain.
3. To think about or explore in depth, to get to the bottom of, esp. to plumb the depths of.
4. To use a plumb bob as a measuring or aligning tool.
5. To accurately align vertically or horizontally.
6. To seal something with lead.
7. : To work as a plumber.
8. To fall or sink like a plummet.
9. To trace a road or track; to follow it to its end.
10. To position vertically above or below.