/ Dictionary / Index L lost motion: Meaning and Definition of Find definitions for: lost' mo'tion Pronunciation: [key] — Mach. Mach. motion of a machine or mechanism, esp. a reciprocating one, during which no useful work is performed. motion between parts in an assembly due to manufacturing tolerances, adjustments, slip, or wear. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. Lost Generation Lost Pleiad 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