Linguistic puns, riddles, and jokes in LotR, etc.

[Finwe]

Actually, I'm surprised that the whole Elrond/Elros discovery slipped my mind. That did indeed play a great part in their naming. I think that Elros's name can also be taken a little deeper. His name means "Star-foam." Waves have foam don't they? Elros became the King of the Mariner-Kingdom, Numenor. Perhaps Tolkien wanted to "prepare" him for his later role.
Another reason why both Elrond and Elros' names start with "El-" is that, considering the theory that it was Earendil himself who named them before leaving on the Quest of Eldamar (as I like to call it), and wanted to keep their names close to that of their mother, Elwing. He also probably wanted to keep their names close to those of Elwing's lost brothers, Elured and Elurin, and of Elu Thingol, the King of the Sindar. After all, the little twins had quite a lineage.