/ Dictionary / Index I illinium: Meaning and Definition of Find definitions for: il•lin•i•um Pronunciation: (i-lin'ē-um), [key] — n. Chem. promethium. Symbol: Il Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. ill-informed Illinoian Related Content Daily Word Quiz: spectral Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language