[usually singular] touchstone (of/for something) (formal) something that provides a standard against which other things are compared and/or judged the touchstone for qualityExtra examples Grammar was regarded as the touchstone of all language performance. He has been a guiding beacon in my life and a touchstone of human integrity. She remained for them a touchstone of good sense. The nineteenth-century struggle to reconstitute Poland was a touchstone for liberals and socialists alike. The way medicines are sold has become one of the touchstone issues of modern capitalism.