Whetstone (noun)

A flat stone used for sharpening knives, tools, or other cutting instruments.

Origin:

From old english "hwætstān" meaning "sharpening stone".

Examples:

1. He sharpened his knife on the whetstone before he went hunting.
2. The whetstone is an essential tool for keeping your knives sharp.
3. I used a fine-grit whetstone to sharpen my chef's knife.
4. The whetstone is made of a hard abrasive material that can sharpen even the dullest blades.
5. I always keep a whetstone in my toolbox to keep my tools in good condition.