Definition of grauwacke in US English:

grauwacke

noun

Geology
  • Greywacke.

Origin

Late 18th century; earliest use found in Richard Kirwan (1733–1812), chemist and mineralogist. From German Grauwacke from grau + Wacke.

Pronunciation

grauwacke

/ˈɡraʊˌwakə/