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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.
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.