/ Dictionary / Index M mesoblast: Meaning and Definition of Find definitions for: mes•o•blast Pronunciation: (mez'u-blast", mes'-, mē'zu-, -su-), [key] — n. Embryol. the mesoderm. the primordial middle layer of a young embryo before the segregation of the germ layers, capable of becoming the mesoderm. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: mesoblast (Thesaurus) mesoappendix mesocardium Related Content Daily Word Quiz: philtrum Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language