The story of the legendary Wampus Cat of various parts of the United States is treated elsewhere on this website. However, John Hairr in his book Monsters of North Carolina, points out that the term wampus or wampus cat can be found used for a variety of unknown creatures as well as the classic Wampus Cat. He is not sure where the term comes from, but he thinks it may be of Scottish origin, because of the considerable number of Scottish settlers in regions where it is used. Scots was in the Middle Ages a separate language from English, but now has merged with it.
This must remain in the realm of uncertainty. There is a North Carolina word wampus meaning crooked and also an odd person, perhaps somewhat thuggish. Scots itself, as far as I know, does not have wampus but I cannot vouch with certainty for its non-existence. It does have a verb wampish, to wriggle.
However, I think the most likely origin of the word is from catawampus which was used to mean a scary creature or being, perhaps preternatural. This is possibly a word of American origin, perhaps just made up. Beyond this, I cannot go.