/ Dictionary / Index L logical sum: Meaning and Definition of Find definitions for: log'ical sum' Pronunciation: [key] union (def. 10a). Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. logical positivism logical syntax Related Content Daily Word Quiz: tactful Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language