Definition of "keystone" in English

noun

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

2. Something on which other things depend for support.

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.

verb

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%.