#whetstone  a flat stone for sharpening edged tools or knives
  supertype:  stone  building material consisting of a piece of rock hewn in a definite shape for a special purpose; "he wanted a special stone to mark the site"
  subtype:  hone  a whetstone made of fine gritstone; used for sharpening razors
  subtype:  oilstone  a whetstone for use with oil

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