keystone

noun

1. The top stone of an arch.

   “The tunnel, which is 1,000 yd. long, had been closed to passenger traffic since November 17, 1949, after some of the keystones had worked loose.”

2. Something on which other things depend for support.

   “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 retail price that is double the cost price; a markup of 100%.
4. 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)To double the cost price in order to determine the retail price; to apply a markup of 100%.

name

1. A census-designated place in Colorado.
2. A city and town in Iowa.
3. A ghost town in North Dakota.
4. A town in South Dakota.