undeadly
Not subject to death; immortal.
"The soul also hath her death, namely, when it lacketh and is destitute of the eternal and godly life, which truly and justly is called the life of the soul: but undeadly or immortal is it called, because it never ceaseth to live, how miserable soever the life of it be. [...]"
Of or pertaining to the undead.
Where it comes from
From Middle English undedly, undeedly, undedlich, from Old English undēadlīc (“immortal, for all eternity”), equivalent to undead + -ly.
Adapted from the Wiktionary entry undeadly (CC BY-SA 4.0).