The Collaborative International Dictionary of English v.0.48:

Immortality \Im`mor*tal"i*ty\, n.; pl. Immortalities. [L.
   immortalitas: cf. F. immortalit['e].]
   1. The quality or state of being immortal; exemption from
      death and annihilation; unending existance; as, the
      immortality of the soul.
      [1913 Webster]

            This mortal must put on immortality.  --1 Cor. xv.
                                                  53.
      [1913 Webster]

   2. Exemption from oblivion; perpetuity; as, the immortality
      of fame.
      [1913 Webster]

WordNet (r) 3.0 (2006):

immortality
    n 1: the quality or state of being immortal [ant: mortality]
    2: perpetual life after death

Moby Thesaurus II by Grady Ward, 1.0:

44 Moby Thesaurus words for "immortality":
   afterlife, animal spirits, animate existence, animation, athanasia,
   athanasy, being alive, birth, deathlessness, eternal life,
   eternal youth, everlastingness, existence, fountain of youth,
   having life, heroic legend, immortal name, imperishability,
   impregnability, incorruptibility, incorruption, indelibility,
   indestructibility, ineffaceability, ineradicability,
   inerasableness, inexpugnability, invincibility, invulnerability,
   legend, life, lifetime, liveliness, living, long life, longevity,
   memory, remembrance, spriteliness, undying fame, undyingness,
   viability, vitality, vivacity



Easton's 1897 Bible Dictionary:

Immortality
   perpetuity of existence. The doctrine of immortality is taught
   in the Old Testament. It is plainly implied in the writings of
   Moses (Gen. 5:22, 24; 25:8; 37:35; 47:9; 49:29, comp. Heb.
   11:13-16; Ex. 3:6, comp. Matt. 22:23). It is more clearly and
   fully taught in the later books (Isa. 14:9; Ps. 17:15; 49:15;
   73:24). It was thus a doctrine obviously well known to the Jews.

     With the full revelation of the gospel this doctrine was
   "brought to light" (2 Tim. 1:10; 1 Cor. 15; 2 Cor. 5:1-6; 1
   Thess. 4:13-18).


The Devil's Dictionary (1881-1906):

IMMORTALITY, n.

    A toy which people cry for,
    And on their knees apply for,
    Dispute, contend and lie for,
        And if allowed
        Would be right proud
    Eternally to die for.
                                                                  G.J.