whitening stone

from The Collaborative International Dictionary of English v.0.48

Whitening \Whit"en*ing\, n.
   1. The act or process of making or becoming white.
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   2. That which is used to render white; whiting. [R.]
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   {Whitening stone}, a sharpening and polishing stone used by
      cutlers; also, a finishing grindstone of fine texture.
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