n. 1 weight, (plumb-)bob, plummet, lead, sinker The plumb holds the string taut and exactly vertical
adj. 2 vertical, perpendicular, straight up and down Make sure the jamb is plumb before hanging the door
adv. 3 vertically, perpendicularly, straight up and down The cord doesn't hang plumb because the shelf is in the way 4 exactly, precisely, dead, right, accurately, Colloq slap, Brit bang, spot The navigator checked our position and we were plumb on course
v. 5 sound, fathom, measure, probe, explore, measure, gauge, delve, penetrate The bathyscaphe has plumbed the deeps of the Indian Ocean I plumb the depths of depression thinking of starving people everywhere.