If you have any context or more information about where you encountered this word, it might be possible to figure out its intended meaning.
For example, it could be:
* A misspelling of a real word: Perhaps you meant "rusticism", which refers to the quality of being rustic or simple.
* A neologism: Someone might have created the word to describe a specific concept or idea.
* A joke or a play on words: It could be a humorous invention for a particular situation.
Please provide more context so I can help you understand the intended meaning of "Rustilismus".