Definition of gneiss noun from the Oxford Advanced Learner's Dictionary

 

gneiss

 noun
noun
BrE BrE//naɪs//
 
; NAmE NAmE//naɪs//
 
[uncountable](geology)
 
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a type of metamorphic rock formed at high pressure and temperature deep in the ground Word Origin mid 18th cent.: from German, from Old High German gneisto ‘spark’ (because of the rock's sheen).
See the Oxford Advanced American Dictionary entry: gneiss