Whet slate

from The Collaborative International Dictionary of English v.0.48

Whet \Whet\, n.
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   1. The act of whetting.
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   2. That which whets or sharpens; esp., an appetizer. "Sips,
      drams, and whets." --Spectator.
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   {Whet slate} (Min.), a variety of slate used for sharpening
      cutting instruments; novaculite; -- called also {whetstone
      slate}, and {oilstone}.
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