/ Dictionary / Index L lethal gene: Meaning and Definition of Find definitions for: le'thal gene' Pronunciation: [key] — Genetics. Genetics. a gene that under certain conditions causes the death of an organism. Also called Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. lethal chamber lethargic Related Content Daily Word Quiz: persevere Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language