keystone

key +‎ stone

Definition 4 (retail) possibly originated in the jewelry industry in the magazine called "Jewelers' Circular-Keystone".[1]

• IPA^(key): /ˈkiː.stəʊn/

keystone (plural keystones)

1. (architecture) The top stone of an arch.
2. 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.

3. A native or resident of the American state of Pennsylvania.
4. (retail) A retail price that is double the cost price; a markup of 100%.
5. (baseball) The combination of the shortstop and second baseman.

keystone (third-person singular simple present keystones, present participle keystoning, simple past and past participle keystoned)

1. (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.
2. (transitive, retail) To double the cost price in order to determine the retail price; to apply a markup of 100%.

• keynotes, keytones