a thick disc of stone or other abrasive material mounted so as to revolve, used for grinding, sharpening, or polishing metal objects
(打磨、抛光金属物件的)磨石;砂轮。
〈罕〉 同<Bold>MILLSTONE</Bold>.
-
keep one's nose to the grindstone work hard and continuously 一刻不停地拼命干