An Annux is a ruler who is considered higher than all others, as mentioned in the book The King of Attolia. The term is derived from the Greek Anax, which means king.
By deferring his sovereignty of Sounis to Attolis and that of Eddis's sovereignty impending their marriage, Sophos effectively makes Eugenides the annux of the three nations at the conclusion of A Conspiracy of Kings.
In Thick as Thieves, Eugenides is called Annux by Kamet during a public audience of the king, wishing to flatter him with the archaic term meaning "great king". Kamel was probably the first to call him so in an official occasion, and that gave him his new name: Kamet e dai Annux - Kamet Kingnamer.