All 3 Uses

immortal
in
Nature, by Emerson
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Here no history, or church, or state, is interpolated on the divine sky and the immortal year.†
*
It is a long way from granite to the oyster; farther yet to Plato,[508] and the preaching of the immortality of the soul.†

immortality = eternal life (to live forever)
And the knowledge that we traverse the whole scale of being, from the center to the poles of nature, and have some stake in every possibility, lends that sublime luster to death, which philosophy and religion have too outwardly and literally striven to express in the popular doctrine of the immortality of the soul.†

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)
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.