A grindstone is a flat, circular wheel made of rough stone that spins on an axle. For centuries, people used grindstones to sharpen metal tools like axes, knives, and scissors. You hold the blade against the spinning stone, and the rough surface grinds away tiny bits of metal until the edge becomes sharp again. The friction creates sparks and a distinctive grinding sound.

Before power tools existed, many farms and workshops had a grindstone, often powered by a foot pedal or hand crank. Blacksmiths and farmers depended on them to keep their tools in working condition. While modern electric sharpeners have largely replaced them, some craftspeople still prefer traditional grindstones for precision work.

The phrase keep your nose to the grindstone means to work hard and stay focused on your tasks, like a craftsperson bent over their work, concentrating intently. If someone tells you they've been keeping their nose to the grindstone, they mean they've been working steadily and seriously, perhaps studying for exams or practicing a difficult skill. The image suggests sustained effort rather than quick bursts of energy.