All 5 Uses of

immortal
in
Don Quixote

and if the might of your strong arm corresponds to the repute of your immortal fame, you are bound to aid the helpless being who, led by the savour of your renowned name, hath come from far distant lands to seek your aid in her misfortunes.†
Chpt 1.29-30 *

Blest souls, that, from this mortal husk set free, In guerdon of brave deeds beatified, Above this lowly orb of ours abide Made heirs of heaven and immortality, With noble rage and ardour glowing ye Your strength, while strength was yours, in battle plied, And with your own blood and the foeman's dyed The sandy soil and the encircling sea.†
Chpt 1.39-40

immortality = eternal life (to live forever)

I am a knight-errant, and not one of those whose names Fame has never thought of immortalising in her record, but of those who, in defiance and in spite of envy itself, and all the magicians that Persia, or Brahmans that India, or Gymnosophists that Ethiopia ever produced, will place their names in the temple of immortality, to serve as examples and patterns for ages to come, whereby knights-errant may see the footsteps in which they must tread if they would attain the summit and crowning point of honour in arms.†
Chpt 1.47-48

I know, as our great Castilian poet says, that— It is by rugged paths like these they go That scale the heights of immortality, Unreached by those that falter here below.†
Chpt 2.5-6

All these and a variety of other great exploits are, were and will be, the work of fame that mortals desire as a reward and a portion of the immortality their famous deeds deserve; though we Catholic Christians and knights-errant look more to that future glory that is everlasting in the ethereal regions of heaven than to the vanity of the fame that is to be acquired in this present transitory life; a fame that, however long it may last, must after all end with the world itself, which has its own appointed end.†
Chpt 2.7-8

Definitions:

(1) (immortal)
living or existing forever

or:

someone famous throughout history

or:

someone who will never die -- such as a mythological god
(2) (meaning too rare to warrant focus)
meaning too rare to warrant focus:

More rarely, "The Immortals" denotes a military corps of the Persian Empire. The Immortals were so-named because each time a member of the 10,000 man corps was killed or seriously wounded, he was replaced by another man. They are best remembered in western culture for their role in defeating the badly out-numbered Spartans at the Battle of Thermopylae.