Copyright infringement wouldn't be the problem since a single word is not generally considered sufficiently creative to be copyrightable in the first place. Trademark infringement, however, could be. Trademarks are all about consumer confusion. If a court finds that your Eberon is "confusingly similar" to Eberron and that the two have the same source, then you would be infringing. Since I had never heard of Eberron before today, I would not be the relevant person to ask, but that fact that someone here noticed and pointed out the possible confusion is pretty good evidence that a court would do the same.