/ Dictionary / Index A alluvial plain: Meaning and Definition of Find definitions for: allu'vial plain' Pronunciation: [key] a level or gently sloping surface formed of sediments laid down by streams, generally during flooding. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. alluvial fan alluvion Related Content Daily Word Quiz: soporific Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language