hwetstan

Old English hwettan meant "to sharpen" and hwetstan was the stone used for sharpening—literally a "sharp-stone." The root is Proto-Germanic *hwatjan, related to "what" in the sense of "keen" or "sharp." The whetstone is among the oldest tools in continuous human use. Neolithic peoples sharpened flint and obsidian on sandstone. Bronze Age smiths used whetstones on their soft metal blades. Viking whetstones have been found across Scandinavia, often worn smooth from years of use.

The geology of whetstones matters. Arkansas novaculite—a microcrystalline quartz found in the Ouachita Mountains—produces some of the finest natural whetstones in the world. Japanese water stones, cut from sedimentary deposits in Kyoto Prefecture, are prized for their ability to produce extremely fine edges. Belgian coticule, quarried near Vielsalm since Roman times, is used for sharpening razors. Each region's geology created a local sharpening tradition.

The Viking trade in whetstones was extensive. The Eidsborg quarry in Telemark, Norway, produced whetstones that have been found as far away as York, Dublin, and Novgorod. A good whetstone was worth trading over thousands of miles because sharp tools saved time and effort in every task from butchering to carpentry. The whetstone was the tool that maintained all other tools.

The metaphorical sense—"to whet the appetite"—appeared by the 16th century. To whet was to sharpen, to make keen, to bring to an eager edge. The image is precise: appetite, like a blade, can be dull or keen, and something (a smell, a taste, a glimpse) can run it across a stone and restore its edge. The metaphor survives even as most people have never touched an actual whetstone.