Grindstone (noun)

1. A flat circular stone that revolves and is used for grinding, sharpening, or polishing.
2. A tool used for grinding or sharpening.

Origin:

From grind + stone, from the action of grinding or sharpening tools on the stone surface.

Examples:

1. The blacksmith used a grindstone to sharpen his tools.
2. He put the knife on the grindstone and began to sharpen it.
3. Grindstones are commonly used to sharpen knives and other cutting tools.
4. Grindstones are also used for polishing surfaces, such as in the case of a grinding wheel for metalworking.
5. The term grindstone can also refer to the tool as a whole, which includes the stone and the mechanism for turning it.