"Deathless" is a translation for the Pali word "amata." It's in the same construction as "anatta." (The "n" is added to the "a-" prefix before a vowel.)
I think people usually read the "deathless element" as an element which doesn't die... but I think it might be inaccurate.
Another way of reading it might be that it's an element which has nothing to do with death, or doesn't have the "death" as a part of it... just like "all dhammas are anatta" means that these dhammas have nothing to do with self.
"Non-death element" might be a better translation.
That's just the way I see it at the moment... I might be wrong.