plumb rule plum-brown • plumbum · · · Info · Definitions · Characters · · plumb rule · · Text Common · · Latin · · Scripts 10 · · Length 3 · · Syllables Definitions · · · (noun) a plumb line attached to a narrow board. Synonyms: plumb rule. · · Noun Definition 1 Characters · · space U+0020 b latin small letter b U+0062 e latin small letter e U+0065 l latin small letter l U+006C m latin small letter m U+006D p latin small letter p U+0070 r latin small letter r U+0072 u latin small letter u U+0075