* A misspelling: Perhaps it's meant to be "slim" or "slain."
* A regional dialect word: It might be a word specific to a particular region or community.
* A made-up word: Someone could have invented the word for a specific purpose.
To understand what "slinn" means, you need more context. Please provide more information about where you encountered this word, like:
* The sentence or phrase it was used in.
* The source: Was it in a book, online, in conversation?
* The speaker or writer's background: Do they speak a particular dialect?
With more information, I can give you a more accurate answer.