From Latin illūstris + -ous.

• (RP) IPA: /ɪˈlʌs.tɹɪ.əs/
• (America) IPA: /ɪˈlʌs.tɹi.əs/, /-ˈləs-/

illustrious

1. Admired, distinguished, respected, or well-known. [from mid 16th c.]
   • 1712 January 2 (Gregorian calendar), [Joseph Addison; Richard Steele et al.], “SATURDAY, December 22, 1711”, in The Spectator, number 255; republished in Alexander Chalmers, editor, The Spectator; a New Edition, […], volume III, New York, N.Y.: D[aniel] Appleton & Company, 1853, →OCLC ↗, pages 127–128 ↗:

     A solid and substantial greatness of soul looks down, with a generous neglect, on the censures and applauses of the multitude, and places a man beyond the little noise and strife of tongues. Accordingly we find in ourselves a secret awe and veneration for the character of one who moves above us, in a regular and illustrious course of virtue, without any regard to our own good or ill opinions of him, to our reproaches or commendations.

     The spelling has been modernized.

   • 1843 December 18, Charles Dickens, “Stave Five. The End of It.”, in A Christmas Carol. In Prose. Being a Ghost Story of Christmas, London: Chapman & Hall, […], →OCLC ↗, page 154 ↗:

     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!

• forgotten
• overlooked
• unadmired
• undistinguished
• unrespected

• lustrious

• French: illustre
• German: glorreich, erlaucht (dated)
• Italian: famoso
• Portuguese: ilustre
• Russian: знамени́тый
• Spanish: ilustre, ínclito (formal), preclaro