Speaking of Keystone – when some anons weren't fond of "QNN" resembling cnn, was looking for Q-words yesterday to substitute. Found this:
The definition of quoin, the meaning of the word Quoin:
Is quoin a scrabble word? Yes!
• n. - The keystone of an arch
• n. - (architecture) solid exterior angle of a building; especially one formed by a cornerstone
Just another synchronicity, sorry for sliding.