slate-grey s of the color of slate or granite Usage(s) New buildings loom high against the slate-grey winter waters of Lake Michigan. Last week Luftwaffe planes spotted a huge Allied convoy specking the slate-grey sea between Iceland and Norway's North Cape. There was a constant roar from bulldozers and heavy-duty trucks churning up the slate-grey earth as they carried dirt and rocks to the growing wall. Synonym(s) slate-gray slaty-grey slaty-gray slaty slatey stone-grey stone-gray