/ Dictionary / Index I international atomic time: Meaning and Definition of Find definitions for: interna'tional atom'ic time' Pronunciation: [key] a system of measuring time based on atomic clocks that measure the second as defined as the SI unit of time. Abbr.: IAT Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. International Association of Lions Clubs International Bank for Reconstruction and Development 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