It is not a prefix, not used as such in English. It must be a mistake by Adria ("locality of Rovigo, Italy", "main-belt asteroid"). Yes there was in the Illyrian Etruscan an adur- component related to the sea, to water, from which the Hadri-Latin is supposed to come, but which was already used as relative to the settlement of Hadria, Hadri or Atri, which according to some Roman authors comes from the name of the Adriatic Sea, although it may be just the other way around. See Adrian , Abdera .
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