Here is a specific example. this page describes several inscriptions to, and two depictions of, a deity called Cocidius (in one inscription, Mars Cocidius, and in another from a different findspot, Silvanus Cocidius). That page states that Cocidius is Germanic.

Other pages describe Cocidius as a Celtic deity, and the shield he holds seems to be of typical first century Celtic pattern. The inscriptions themselves are in Latin so tell us nothing of the origion. We could make reasonable cases for the word Cocidius being Gaulish or, I suspect, protoGermanic.

I would be interested to hear linguistic arguments either way, also if anyone has any continental occurences of this name (all the ones I have see are north-west England, along Hadrians wall and south-west along the coast to north Wales).