A whetstone is a smooth, flat stone used to sharpen the blade of a knife, ax, or other cutting tool. When you rub a dull blade against a whetstone at the right angle, tiny particles of stone grind away at the metal, creating a sharp new edge. Think of it like using sandpaper to smooth rough wood, except you're working with metal instead.

For thousands of years, before anyone could buy a new knife at a store, people depended on whetstones to keep their tools sharp. A dull knife makes cutting harder and more dangerous because you have to press harder and the blade can slip. A sharp blade, maintained with a whetstone, cuts cleanly and safely through whatever you're working on.

Many people wet their whetstones with water or oil before using them. The liquid helps the stone work better and washes away metal particles.

You might hear someone say that competition or challenge serves as a whetstone for skills or character. Just as a whetstone sharpens a blade, difficult experiences can sharpen your abilities. A tough math problem might be a whetstone for your problem-solving skills, or a talented opponent might be a whetstone that improves your performance.