I need to know how you would address the High King of Ireland (Ard rí na hÉireann). Basically, if you met him face to face, what would you call him. Your Majesty? I'm not interested in the English translation but in the "original" honorific, so to speak.
For this, setting and time don't matter due to plot complications. As long as someone, somewhere, at sometime, addressed the High King by that honorific I'm satisfied. I would also be interested in knowing if anyone nowadays would recognize the honorific, since my readers happen to live at this time. And of course if the meaning has changed to a "chair" or something, do inform me.