whetstone

In 1557, the Whetstone of Witte, an English algebra text, introduced the modern equal symbol.

When using a whetstone, you’ll have to flip the blade over to sharpen both sides, but it’ll work perfectly well.

There are electric sharpeners, two-stage hand sharpeners, and whetstones.

Even the best whetstones aren’t very expensive, but you can opt for a double-sided one for under $25.

The clever design of this knife sharpening stone allows you to simply flip the whetstone sharpener over to go from rough to fine.

He approved of Parpon, and never lost a chance of sharpening his humour on the dwarf's impish whetstone of a tongue.

Behind him, each of the natives had laid his stabbing-knife, skinning-knife, and whetstone.

It's colder'n a blue whetstone, so put on all the clothes you've got.

It is a profession which uses the conscience as a whetstone upon which to sharpen the intellect.

His firm and close-grained mind was a sort of whetstone on which my father sharpened his wits at this weekly setting.