(architecture) The top stone of an arch.
Something on which other things depend for support.
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.
Knocking out one keystone species, like Atlantic Cod, can destabilize an entire ecosystem.
In food webs, you have a few keystone species like Atlantic cod that connect hundreds of predators and prey.
