Top Definition
Luminous colours which are particularly bright and garish and are used in appropriate circumstances, resulting in mild nausea for the observer.
"Did you see that woman's fluorescent pink lipstick?"

"Yeh... it was illuminous..."
by SimonC June 08, 2007
1 more definition
The Mac OS X Leopard GUI.
Wow, looks like you're running Illuminous on your Mac.
by Jonathan Neal December 12, 2006

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