(plum) noun
1. A lead weight on the end of a line used by masons, carpenters, etc., to find the exact perpendicular; a plumb bob; a plummet.
2. A plummet or nautical sounding lead; a sinker on a fishing line, etc.
—off (or out of) plumb Not exactly vertical; not in alinement.
—adjective
1. True, accurate, and upright; vertical or perpendicular; hence, figuratively, upright in principle.
2. Colloq. Sheer; complete: also plum.
—adverb
1. In a line perpendicular to the plane of the horizon; vertically.
2. Colloq. With exactness; correctly; exactly; completely; entirely: also plum.
—v.t.
1. To test the perpendicularity of with a plumb.
2. To make vertical; straighten: usually with up.
3. To test the depth of; sound.
4. To reach the lowest level or extent of; fathom: to plumb the depths of despair.
5. To seal with lead. ♦ Homophone: plum. [<F plomb <L plumbum lead]

Var. of PLUMBO–.