I didn't use the word. The bible did. Here's the greek word that's translated as "immortality" in the bible:
From Thayers Lexicon:
athanasia
Thayer Definition:
1) undying, immortality, everlasting
Strongs G110:
athanasia
From a compound of G1 (as a negative particle) and G2288; deathlessness: - immortality.
This same word is used by Paul in 1 Corinthians.
1Co 15:51 Behold, I tell you a mystery; we will not all sleep, but we will all be changed,
1Co 15:52 in a moment, in the twinkling of an eye, at the last trumpet; for the trumpet will sound, and the dead will be raised imperishable, and we will be changed.
1Co 15:53 For this perishable must put on the imperishable, and this mortal must put on immortality.
1Co 15:54 But when this perishable will have put on the imperishable, and this mortal will have put on immortality , then will come about the saying that is written, "DEATH IS SWALLOWED UP in victory.
So you see, there is nobody immortal, not subject to death, except for Christ. Christians become immortal at the return of Christ (at the last trumpet, reference Rev. 11:15). That's what the bible says. Traditional Christianity teaches that the saved and the unsaved are already immortal.
Another scripture that I found today:
Eze 33:11 Say unto them, As I live, saith the Lord GOD, I have no pleasure in the death of the wicked; but that the wicked turn from his way and live: turn ye, turn ye from your evil ways; for why will ye die, O house of Israel?
Note that God says that the fate of the wicked IS death, while the fate of the saved is to live. Clearly both the wicked and the saved die a physical death. But the saved go on to immortal life, while the wicked go to the second death.
The wicked SURELY die.
Christ died.
Seems you're simply not distinguishing between the death of the body and the death of the soul.