Erathoniel is modified Sindarin Elvish (Tolkeinian), and it has no literal meaning. It is pronounced Era-thon-iel (like marathon, with an -iel). It is a pseudonym.
If you wish to shorten it, its familiar form is Era, not Erath. That makes me think you made a typo of "wrath". Erath seriously bugs me, because it breaks up the syllables. Yeah, that's all it takes. Era also saves you two letters of type.
Hey, you asked. Don't blame me.