/ Dictionary / Index M marginal cost: Meaning and Definition of Find definitions for: mar'ginal cost' Pronunciation: [key] the cost of one additional unit of any item produced or bought in quantity. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. marginal marginalia Related Content Daily Word Quiz: bungled Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language