Definition 4 (retail) perhaps originated in the jewelry industry in the magazine called "Jewelers' Circular-Keystone" Source: https://english.stackexchange.com/questions/341864/what-is-the-source-of-the-word-keystone-in-reference-to-pricing-a-product
keystone (plural keystones)
- (architecture) The top stone of an arch.
- Something on which other things depend for support.
- 1999, Eliezer Geisler, Methodology, Theory, and Knowledge in the Managerial and Organizational ...:
- Tension between empirical and theoretical knowledge is keystone to sociological and to organizational theories, as early as in Marx's and Weber's frameworks.
- A native or resident of the American state of Pennsylvania.
- (retail) A retail price that is double the cost price; a markup of 100%.
- (baseball) The combination of the shortstop and second baseman.
- (transitive) To distort (an image) by projecting it onto a surface at an angle, which for example causes a square to look like a trapezoid.
- (transitive, retail) To double the cost price in order to determine the retail price; to apply a markup of 100%.