Meaning: declaratory (obs.); nominal(obs.); spoken instead of written, as a will (legal). That's from the 1913 Webster. Funny chiasmus in the changing meanings of this word; it's gotten more solid about being immaterial.
From Latin translated as "nominal". Did that mean to them what it does to us? My little Junior Classic Latin Dictionary has nuncupo, to call, to name; to proclaim, to appoint. Hunh. If naming someone appoints them to office, and and having office is regarded as a real thing, then it doesn't mean (as it often does to us) being something only in name. I have recently been vexed by nominal dimensions in lumber, because I am trying to repair something built with wood of the actual dimensions we now only name things by. Nothing like a black dusty half-inch physical gap to remind one that names can outlast their meanings.
Judging, inexpertly, from the uses cited in the OED, "nuncupatory" has gone down in the world as the spoken word has. In 1609, writing probably about the ancient world, an imperial throne was bestowed nuncupatively;
in 1651 "Lands cannot be given by a nuncupative will"; soldiers and sailors can make them, though. "Soi-disant" implies that no-one else would say so; "nuncupative" is a little more polite?
Or I'm leaning too much on this because I have been wallowing through the seas of the Elder Edda, which has lengthy catalogues just explained to me as "mnemonic ... primitive belief that knowledge of the proper name for a thing gives the knower the ability to evoke the object, or its power." But in Germanic, look you, and it lasted longer where the Latin-speaking clergy came late. That's an odd one for Harry Potter consistency arguments.