The Collaborative International Dictionary of English v.0.48:
Illustriousness \Il*lus"tri*ous*ness\, n. The state or quality of being eminent; greatness; grandeur; glory; fame. [1913 Webster]WordNet (r) 3.0 (2006):
illustriousness n 1: the property possessed by something or someone of outstanding importance or eminence [syn: greatness, illustriousness]