Definition of orthogneiss in US English:

orthogneiss

noun

Geology
  • A form of gneiss derived by metamorphism from igneous rocks.

Origin

Early 20th century; earliest use found in Alfred Harker (1859–1939), petrologist. From ortho- + gneiss, after German Orthogneiss.

Pronunciation

orthogneiss

/ˈɔːθə(ʊ)nʌɪs/