The Collaborative International Dictionary of English v.0.48:
Illustriously \Il*lus"tri*ous*ly\, adv. In a illustrious manner; conspicuously; eminently; famously. --Milton. [1913 Webster]WordNet (r) 3.0 (2006):
illustriously adv 1: in an illustrious manner; "Einstein, the illustriously famous physicist of the 20th century"