burrstone

/ˈbɜrˌstoʊn/
noun
  1. A hard, rough stone used for grinding grain, especially in a mill.
    • The museum displayed a massive burrstone from a 19th-century gristmill.
    • Burrstone wheels were essential for sharpening tools in the past.
    • The old mill still uses a burrstone to grind wheat into flour.
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