Qua

The best literal definition I've seen is "in the capacity of." It would also translate to "as." And I was wrong when I said it derives from "what" in Latin. It actually derives from "who." Here are some examples of its usage I found on the internets:

"It was qua poet that Byron resurrected the exploded and discarded immortal Christian soul by bodying it forth through the notion of soul conceived as poetic imagination."

"The President qua head of the party mediated the dispute."

"Their old standing friends, qua individuals and groups, have to unite and wage a worldwide campaign that should equal the protests that are being made against G8, WTO, IMF, and the World Bank."

"The self-perpetuating tendencies of educational institutions, qua institutions, should never go unchallenged when they perpetuate socially disputable functions."