Question: I am writing a story that is sort of magical realism/scifi. I had an idea of incorporating homeless cats into the plot based on a children's book I read, and then I had this brilliant idea of having the characters become the cats by crawling into their cat skins. Then, I realized I had read a different scifi story once about people putting on cat skins and becoming cats. Now I'm worried I am stealing the idea. The stories are completely different, but is even using the term "cat skin" too close? I'm not worried about the general idea of people becoming cats, but more so about using the phrase "cat skin" - is that too close? Do I have to use a different phrase? Beyond this phrase, the stories, as I said, are completely different. Answer:
As always, I am not a lawyer and cannot give legal advice. Fortunately, few books make enough money to be worth anyone's while to file a lawsuit, though there are exceptions.
That said... To protect yourself, you should abstain from using another writer's made-up terminology and phrases, if they are found in works that are still under copyright (generally up to 50-75 years after the writer has died).
In this case, I think you should do a little research to see if there are myths, fables, fairy tales, etc. that are in public domain that use this idea of people putting on animal skins and becoming animals. If you find ancient folklore about people using "cat skins" for such transformations, that would help your case -- more so if you can find public domain stories in English that use the phrase. If you can, that would show the phrase, used this way, is in public domain and not entitled to copyright protection. (At least IMHO, but if you're worried check with a lawyer.)
At the very least, researching ancient stories about people turning into cats or other animals could give you more ideas for your story.
Best of luck.