/ Dictionary / Index F fifth dimension: Meaning and Definition of Find definitions for: fifth' dimen'sion Pronunciation: [key] — Math., Physics. Math.,Physics. a theoretical dimension beyond or in addition to a fourth dimension. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. Fifth Commandment fifth estate Related Content Daily Word Quiz: modify Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language