Wikipedia
Sharpening stones, water stones or whetstones are used to grind and hone the edges of steel tools and implements.
Examples of items that may be sharpened with a sharpening stone include scissors, scythes, knives, razors and tools such as chisels, hand scrapers and plane blades. Though it is sometimes mistaken as a reference to the water often used to lubricate such stones, the word "whetstone" is a compound word formed with the word "whet", which means to sharpen a blade, not the word "wet". The process of using a sharpening stone is called stoning.
Usage examples of "sharpening stone".
He sat with his back against a tree, sliding a sharpening stone along his sword and watching Rand.
He took a sharpening stone from his pack and ran it along the edge of the largest knife with a repeated wheeping sound.
He then fetched a bit of oil and a sharpening stone from his things and, returning to his place, removed his sword from its scabbard.
I dropped the sharpening stone and tried to put away my sword, wasting precious seconds.