/ Dictionary / Index I IU: Meaning and Definition of Find definitions for: IU Pronunciation: [key] immunizing unit. international unit. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. -ity IUD Related Content Daily Word Quiz: acquiesce Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language