/ Dictionary / Index E embryo sac: Meaning and Definition of Find definitions for: em'bryo sac" Pronunciation: [key] — Bot. Bot. the megaspore of a seed-bearing plant, situated within the ovule, giving rise to the endosperm and forming the egg cell or nucleus from which the embryo plant develops after fertilization. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. embryonic membrane embryotomy Related Content Daily Word Quiz: soporific Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language