/ Dictionary / Index D dual space: Meaning and Definition of Find definitions for: du'al space' Pronunciation: [key] — Math. Math. the set of all linear functionals whose domain is a given vector space. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. dual-purpose Duane Related Content Daily Word Quiz: exemplary Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language