1. To determine the depth of water with a plumb; that is, "to sound the depths".
2. To test the verticality or alignment of something with a plumb.
3. To straighten or make perpendicular: "The mason will plumb up the chimney to make sure that it is straight."
4. To examine closely or deeply; to probe; that is, to succeed in fully understanding something, especially something mysterious: "The scientist spent his life plumbing the minds of criminals."
5. To seal with lead; for example, to equip something with plumbing, seal pipes with lead, or to work as a plumber: "The plumber is almost finished plumbing her apartment."
6. Etymology: the verbal use in English of "sound the depths" comes from the use of a line weighted with lead (a plumb line) to measure the depth of water and from the use of a similar line to determine the vertical positions of structures, etc.

1. The system of pipes and other apparatus for conveying water, liquid wastes, etc., as in a building: "The house still has too much old plumbing."
2. The work or trade of a plumber; or the work that a plumber does: "His business of plumbing has been going on for about ten years."
3. The act of a person who plumbs; such as, in determining depth: "His recent plumbing of the lake determined how much the water level increased since the flooding."
4. A method used to find a vertical line or to ensure that an object is set straight: "The plumbing of the outer walls showed how crooked they were."
5. The digestive, urinary, and reproductive tracts and organs of the body (slang): "There are all kinds of things that can go wrong with a person's internal plumbing."