/ Dictionary / Index G germ layer: Meaning and Definition of Find definitions for: germ' lay"er Pronunciation: [key] one of the three primary embryonic cell layers. Cf. ectoderm, endoderm, mesoderm. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. Germiston germline insertion Related Content Daily Word Quiz: fidelity Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language