principal diagonal principal axis • principal investigator · · · Info · Definitions · Synonyms · Characters · · principal diagonal · · Text Common · · Latin · · Scripts 18 · · Length 7 · · Syllables Definitions · · · (noun) the diagonal of a square matrix running from the upper left entry to the lower right entry. Synonyms: main diagonal, principal diagonal. · · Noun Definition 1 Synonyms · · · main diagonal · · Synonym 1 Characters · · space U+0020 a latin small letter a U+0061 c latin small letter c U+0063 d latin small letter d U+0064 g latin small letter g U+0067 i latin small letter i U+0069 l latin small letter l U+006C n latin small letter n U+006E o latin small letter o U+006F p latin small letter p U+0070 r latin small letter r U+0072