How the mighty do fall!

[Zigûr]

Originally Posted by William Cloud Hicklin

no Ainu can be killed within Ea.

It depends what you mean by "killed" though, doesn't it? Morgoth was literally killed when he was executed by Mandos at the end of the First Age, as in his body was damaged so much that it stopped working and his fëa could no longer resided within it.

I agree that the case of Sauron was different, however; his body probably fell apart or ceased to exist when the Ring was destroyed, rather than him being "killed" as we understand it; that being said, he was described as having been "slain" at the end of the Second Age.