/ Dictionary / Index S SEIU: Meaning and Definition of Find definitions for: SEIU Pronunciation: [key] Service Employees International Union. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. seismoscope sei whale Related Content Daily Word Quiz: immense Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language