gneiss  (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. |
