The aristocracy - the "big men" - of Celtic society were not titled. Real aristocrats have no titles. Scottish Clan chiefs have no titles as clkan chiefs, even if they also may hold Scottish peerages. A clan chief is simply The Macdonald (or whatever, I may be wrong on the example used)
The only terms I am familiar with are a generic term that is translated as "king" and a term used to denote the leader of a warband
The generic term for "king" in Celtic was rix, the same word as Latin rex. In Ireland a king was known as a tuath. This was also the term used to denote his people.
The leaders of the Celtic warbands that descended on the Classical world in the Century were styled bran or bren which is why the Ancient historians maintain that they were named Brennus. I mdo not know whether Bran as used in Ireland (e.g. Bran mac Morn) was a proper name or just the title given to the warchief/strongman/homicidal maniac of the Morn clan.
But the important thing is that there are no titles in a real aristocracy. Titles imply submission to a higher authority.