Whetstone

(hwet's ton,) [from A. S. hwettan, to give an edge to,] or NOVAUCLITE, [ L. novacula, a whetstone.] (Miner.) So called from its property of whetting or sharpening steel. It is a tal cy slate, containing silica; to the particles of which, though not perceptible, its efficacy is due. [s. 959]