Breadcrumb Home > Dictionary > Index B blastocyst: Meaning and Definition of Find definitions for: blas•to•cyst Pronunciation: (blas'tu-sist), [key] — n. Embryol. the blastula of the mammalian embryo, consisting of an inner cell mass, a cavity, and an outer layer, the trophoblast. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: blastocyst (Thesaurus) blastocoel blastoderm TrendingHere are the facts and trivia that people are buzzing about. Animal Group Terminology Largest Countries in the World (by Area) Current Events This Week: January 2023 State Abbreviations Dinosaur Fossils (By U.S. State!) The Chinese Zodiac ✖ Related Content Daily Word Quiz: locution Analogy of the Day: Today’s Analogy Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language