1. A hard black stone, such as jasper or basalt, formerly used to test the quality of gold or silver by comparing the streak left on the stone by one of these metals with that of a standard alloy.
2. An excellent quality or example that is used to test the excellence or genuineness of others: "the qualities of courage and vision that are the touchstones of leadership" (Henry A. Kissinger).
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2018 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
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