All 3 Uses of

immortal
in
Dracula

When they become such, there comes with the change the curse of immortality.†
p. 229.2 *

immortality = eternal life (to live forever)

Just think what will be his joy when he, too, is destroyed in his worser part that his better part may have spiritual immortality.†
p. 328.9

I know, and you know, that were I once dead you could and would set free my immortal spirit, even as you did my poor Lucy's.†
p. 351.4

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.