Semi serious question, (please do not ask "AI") I can do web searches just fine so please answer from your own experience:

In English, you have "four letter words", these words have four letters but are perhaps not to be used in polite communication.

Are there any other "group of words constrained by arbitrary rules" in other languages?

Mind you, it doesn't have to be an offensive group of words, but more like a grouping outside the traditional language syntax.

#AskFedi