grindstone [ME] A grindstone is a thick revolving disc of stone on which knives and tools are sharpened. If someone makes you work hard and continuously they are keeping your nose to the grindstone. A word related to grind [OE] is grist [OE], ‘corn that is to be ground’. You can describe something which can be turned to good use, such as experience or knowledge, as being grist to the mill [16th]. The phrase comes from the 17th-century proverb all is grist that comes to the mill.