/ Dictionary / Index L life span: Meaning and Definition of Find definitions for: life' span" Pronunciation: [key] the longest period over which the life of any organism or species may extend, according to the available biological knowledge concerning it. the longevity of an individual. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: lifespan (Thesaurus) life-size lifestyle 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