touchstone
UK: ˈtʌtʃstəʊn | US: ˈtʌtʃstoʊn
n. a standard or criterion by which something is judged or recognized
n. (historical) a black stone used to test the purity of gold or silver by rubbing
The word "touchstone" originates from the literal practice of using a dark, fine-grained stone (like basalt or jasper) to test the purity of precious metals. Rubbing gold or silver against the stone leaves a streak whose color reveals its quality. By the 16th century, "touchstone" evolved metaphorically to mean any reliable standard for evaluation. The morphemes reflect this dual history: "touch" (from Old French tochier, meaning "to test by contact") and "stone" (from Old English stān).
Shakespeare’s works are often considered the touchstone of English literature.
The scientist used peer-reviewed studies as her touchstone for accuracy.
In ancient markets, merchants relied on a touchstone to verify gold coins.
His integrity became the touchstone by which others measured their actions.
The new policy failed to meet the touchstone of environmental sustainability.