from The Century Dictionary.
- noun Incapability of dying; immortality.
from Wiktionary, Creative Commons Attribution/Share-Alike License.
- noun The condition of not being
susceptibleto death; immortality.
from Wiktionary, Creative Commons Attribution/Share-Alike License
Undead --- I looked up the term 'undead' in the dictionary, and found that words like 'undeadly' and undeadliness 'were obsolete terms for immortal and immortality.
For as man is a mingled thing of two substances, a bodily and a ghostly, so it needeth for to have two sere  means to come by to perfection;  sith it so is that both these substances shall be oned in undeadliness at the uprising in the last day; so that either substance be raised to perfection in this life, by a mean accordant thereto.
But to meet God! And 'tis no sweven, [dream] ne fallacy, this dread undeadliness [immortality] -- it is real.
He that dwelleth between the terms hath nearhand forsaken deadliness, but not fully, and hath nearhand gotten undeadliness, but not fully; for whiles that him needeth the goods of this world, as meat and drink and clothing, as it falleth to each man that liveth, yet his one foot is in this deadly life; and for great abundance of ghostly joy and sweetness that he feeleth in God, not seldom but oft, he hath his other foot in the undeadly life.
‘undeadliness’ for immortality; ‘uncunningness’ for ignorance;