/ Dictionary / Index I IRS: Meaning and Definition of Find definitions for: IRS Pronunciation: [key] Internal Revenue Service. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: irs (Thesaurus) irruptive Irtysh 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