Addan in the Bible Encyclopedia - ISBE

ad'-an ('addan; in Neh 'addon; connected in some way with the name of the god Addu): A name mentioned in the list of the returning exiles (Ezr 2:59, duplicated in Neh 7:61). It is one of several names of Babylonian localities from which came men who were unable to declare their genealogy as Israelites.

Link: https://bible-history.com/isbe/A/ADDAN/