I would also vote for 'aristocracy' here, because it's the broader term.
Carullus, I don't know where you got the idea that it's used only with regard to government; did you check a dictionary, by any chance? Etymology often doesn't match modern usage 1:1.
escoville or someone may be clearer on this, but as I understand it, royalty are heads of state, and the nobility are their relatives, the royal family, typically with at least the title of Duke. The aristocracy, in contrast, are the next highest class, including lower hereditary titles such as Earl, Marquis, Lord, or in other countries barons or counts. The next class down are (were?) squires, with the title of Sir, who are only gentry, not aristocracy. All Britons below that are just commoners.