Something that's Illustrious is well known or famous, leaving a trail of glory in its wake. An illustrious career, for example, is full of impressive achievements and celebrated contributions to society.
Coming from the Latin illustris, meaning “bright, distinguished, famous,” illustrious is a powerful adjective. It's similar to luster, which is a brilliant shine — so imagine that something illustrious is as wonderful as a sparkling diamond. Use this word to describe the career or reputation of someone really successful, like a bestselling author or business mogul.