Elves: truly immortal?

[Ithaeliel]

WARNING: here follows the interpretations of a very literal person.

When we refer to elves, they are always referred to as 'immortal,' because they will live forever-- if nothing happens to them. But here's something I looked up on that inexpendable dictionary.com that got me thinking:

im·mor·tal (i-môr'tl) One not subject to death.

...and yet we call elves immortal. For one, they are very much subject to death, whether in battle or of grief, and for another, it is stated that the elves will only live until the end. For true immortals, there is no end. They will live on alone and unable to die even if they want to. The Eldar have a choice in the matter. They are not totally immortal; rather they are able to live forever. Any thoughts on this? Or am I reading too much into the word?