illustrious UK /ɪˈlʌs.tɹɪ.əs/US /ɪˈlʌs.tɹi.əs/ adjective1 •Admired, distinguished, respected, or well-known.Really, for a man who had been out of practice for so many years, it was a splendid laugh, a most illustrious laugh. The father of a long, long line of brilliant laughs! — 1843 formsmore illustrious · most illustrious