G0166300 (nīs)n. A banded or foliated metamorphic rock, usually of the same composition as granite.[German Gneis, probably alteration of Middle High German ganeist, spark (from its appearance), from Old High German gneista.]gneiss′ic(nī′sĭk), gneiss′oid′(nī′soid′), gneiss′ose′(nī′sōs′) adj.EncyclopediaSeegneiss