John Kern, a playwright I spoke with tonight--we ushered at The Gingerbread House (which I recommend)--was describing a play he wrote, about teenage clones. He said the play addressed this idea of people's quiddity.
"Wait--liquidity?" I said.
"No," he said. "Quiddity. It's an Old English word. It means essence."
Personally, I think its looks are only so-so but to hear it is nice, and it lies so close to liquidity and yet so far. It's not uninteresting to consider people's liquidity, given how much of the human body is water.