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Definition of TOUCHSTONE

  • a fundamental or quintessential part or feature basis.
  • A piece of fine-grained dark schist or jasper formerly used for testing alloys of gold by observing the color of the mark that they made on it
  • A standard or criterion by which something is judged or recognized
  • a highly siliceous (usu black) stone or other stone for testing gold or silver by the colour of the mark each makes on it; (fig.) a criterion, a standard [n -S]