Board Thread:Lore Discussion/@comment-24640703-20140714030711/@comment-13446185-20140714061602

Ur in TES sort of means "the first" or "original", hence Ur-Tower (Adamantia) original tower, and Ur-Dra (Nocturnal) original Daedra.

Dagoth Ur liked to think of himself as bigger piece of the universe than he really was, he gave himself the title Ur because he believed he was God.