/ Dictionary / Index L least upper bound: Meaning and Definition of Find definitions for: least' up'per bound' Pronunciation: [key] — Math. Math. an upper bound that is less than or equal to all the upper bounds of a particular set. 3 is the least upper bound of the set consisting of 1, 2, 3. Abbr.: lub&hasp; Also called Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. least squares leastways Related Content Daily Word Quiz: arboreal Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language