principal investigator principal diagonal • principality · · · Info · Definitions · Synonyms · Characters · · principal investigator · · Text Common · · Latin · · Scripts 22 · · Length 8 · · Syllables Definitions · · · (noun) the scientist in charge of an experiment or research project. Synonyms: principal investigator, PI. · · Noun Definition 1 Synonyms · · · pi · · Synonym 1 Characters · · space U+0020 a latin small letter a U+0061 c latin small letter c U+0063 e latin small letter e U+0065 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 s latin small letter s U+0073 t latin small letter t U+0074 v latin small letter v U+0076