(+ to) sharing in the knowledge of something secret

was not privy to the conspiracy

archaic secret; private

Is the banquet ready i’ the privy chamber? — Shakespeare

This … diviner … told me what privy marks I had about me, as, the mark of my shoulder, the mole on my neck, the great wart on my left arm — Shakespeare

a small building containing a toilet

somebody who shares a legal interest in a transaction