There are nine meanings listed in oeds entry for the word plumb, two of which are labelled obsolete. (building) a weight, usually of lead, suspended at the end of a line and used to determine water depth or verticality 2. A small mass of lead or other heavy material, as that suspended by a line and used to measure the depth of water or to ascertain a vertical line. Meaning, pronunciation, picture, example sentences, grammar, usage notes, synonyms and more. [countable] building, surveying a small mass of lead hung on a line and used to measure the depth of water or to make sure a line is straight up and down. How to use plumb in a sentence. See examples of plumb used in a sentence. · plumb (third-person singular simple present plumbs, present participle plumbing, simple past and past participle plumbed) to determine the depth, generally of a liquid; To a complete degree completely Definition of plumb verb in oxford advanced learners dictionary. Synonym discussion of plumb. The meaning of plumb is a lead weight attached to a line and used to indicate a vertical direction. Plumb is used to give emphasis to an adjective or verb that describes a feeling or condition. To supply a building or a device with water pipes, or to connect a building or a device to a…. (building) the perpendicular position of a freely suspended plumb line (esp in the … Exactly straight down or up in a perfectly vertical position; See ‘meaning & use’ for definitions, usage, and quotation evidence.