/ Dictionary / Index G gneiss: Meaning and Definition of Find definitions for: gneiss Pronunciation: (nīs), [key] — n. a metamorphic rock, generally made up of bands that differ in color and composition, some bands being rich in feldspar and quartz, others rich in hornblende or mica. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: gneiss (Thesaurus) gnawn gneissoid Related Content Daily Word Quiz: perspicacious Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language