Illustrious means distinguished by outstanding achievement. An illustrious career, an illustrious ancestor, an illustrious name.
It is formal and belongs to obituaries, citations and toasts. Buried in it is the idea of light: the Latin means shining, and an illustrious family is one that casts lustre. Illustrate is the same root, from throwing light on something.
1adjectiveillustriousDistinguished by outstanding achievement.
“The school is proud of its illustrious former pupils, who include two Nobel Prize winners.”
illustrious is a quality.
Latin illustris means bright or distinguished, from illustrare, to light up, from lustrare, to make bright.
Proto-Indo-European
*lewk- — bright; to shine
Latin
illūstris — bright, shining; distinguished, prominent, illustrious
English, today
illustrious
Built from
From Latin illūstris (“bright, shining; distinguished, prominent, illustrious”) + -ous. Illūstris is derived from illūstrō (“to brighten, illuminate; to make famous or illustrious”), from in- (“in, inside”) + lūstrō (“to purify by making a sacrifice; to brighten, illuminate”) (from lūstrō (“purificatory sacrifice”), possibly ultimately from Proto-Indo-European lewk- (“bright; to shine”) or lewh₃- (“to wash”)).
Etymology from Wiktionary, CC BY-SA