"Evil" and "immoral" mean the same thing
No, they don't. Evil is the state of constant and even deliberate immorality, chosen as a direct challenge to "Good".
A person can (hypothetically)
be evil - such a person would consciously elect to take the immoral option over a more moral alternative, because he is fundamentally in favour of immorality of any and all kinds.
A person cannot
be immoral; His actions in a given situation can be, but observing him to choose an immoral action in one circumstance does not allow us to predict that he would choose a different
but always immoral action in a different circumstance, as we could were he "evil".
If John kills his wife because he made an immoral decision to do so, that tells us bupkis about how John would act if he found an unsecured and unguarded bank vault.
If, on the other hand, John killed his wife because he is evil, we can be sure that he would also rob a bank given the opportunity, and would also, if he could, kick a cute puppy, put pineapple on your pizza, and build a doomsday machine to destroy the world.
If you catch a person in an immoral act, you can take steps to educate him into behaving differently the next time he has to choose. He can, in theory, be rehabilitated. But if a person is evil, only execution or life imprisonment could ever protect society from them.
Evil is the absurd, cartoonish, super-exagerated
essense of immorality.
It's not mere immorality, it's defined as irredeemable, uncaring, and unavoidable.
It's one horn of the absurd Abrahamic false dichotomy of the struggle between good and evil (though of course that absurdity pre-dates Abrahamic religion - that's just its current preferred refuge).
No person is evil, just as no person is good. Real people do both moral and immoral things, and are not limited to only one of these two.