Source : Webster's Revised Unabridged Dictionary (1913)

Illustrious \Il*lus"tri*ous\, a. [L. illustris, prob. for
   illuxtris; fr. il- in + the root of lucidus bright: cf. F.
   illustre. See {Lucid}.]
   1. Possessing luster or brightness; brilliant; luminous;
      splendid.

            Quench the light; thine eyes are guides illustrious.
                                                  --Beau. & Fl.

   2. Characterized by greatness, nobleness, etc.; eminent;
      conspicuous; distinguished.

            Illustrious earls, renowened everywhere. --Drayton.

   3. Conferring luster or honor; renowned; as, illustrious
      deeds or titles.

   Syn: Distinguished; famous; remarkable; brilliant;
        conspicuous; noted; celebrated; signal; renowened;
        eminent; exalted; noble; glorious. See {Distinguished},
        {Famous}.

Source : WordNet®

illustrious
     adj 1: widely known and esteemed; "a famous actor"; "a celebrated
            musician"; "a famed scientist"; "an illustrious
            judge"; "a notable historian"; "a renowned painter"
            [syn: {celebrated}, {famed}, {far-famed}, {famous}, {notable},
             {noted}, {renowned}]
     2: having or conferring glory; "an illustrious achievement"
     3: having or worthy of pride; "redoubtable scholar of the
        Renaissance"; "born of a redoubtable family" [syn: {glorious},
         {redoubtable}, {respected}]