GREYWACKE Meaning of GREYWACKE in English n. (US graywacke) Geol. a dark and coarse-grained sandstone, usu. with an admixture of clay. [ Anglicized f. G Grauwacke f. grau grey: see WACKE ] Concise Oxford English dictionary. Краткий оксфордский словарь английского языка. 2012