plumb, plumbed 1. A weight on the end of a line, used to determine water depth. 2. A weight on the end of a line, used especially by masons and carpenters to establish a true vertical. 3. 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. 4. In a verti... Found on http://www.wordinfo.info/words/index/info/view_unit/1705/