/ Dictionary / Index L lost river: Meaning and Definition of Find definitions for: lost' riv'er Pronunciation: [key] a river that flows into an underground passage or sinkhole. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. Lost Pleiad lost tribes Related Content Daily Word Quiz: lunar Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language