Revenant can mean a few things:
A revenant is one who returns after a lengthy absence.
Another type of revenant is a person who returns from the dead (i.e., a ghost), possibly to achieve a specific goal (e.g., taking revenge on their killer). I believe this is the most common form of the word.
Revenant can also be an adjective meaning something typical of a revenant. Of course, since I firmly believe the dead aren't wandering around, I'm not really sure what a typical sound of a dead person would be. However, "revenant shrieks and groans" is one example phrase that should give you a rough idea.
Revenant can also mean returning or recurring. I would guess this is the least common of the four uses.
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