How is [x] used in medieval German?

[Anton]

The word for six, "sex" is a common one indeed, as are certain others like ax and ox. 

I think those are common in English, not in German. The point is that in German the respective common ending is "-hs" or "ck[e]s", but somehow it is changed into "-x".

Now of course the most interesting one is "pox" for "bocks" in Fastnachtspielen. If memory serves, those are also all expletives?

Well yes, that's what I've been posting about.

Yeah but his Latin didn't make much sense

In a charm, it does not necessarily has to. Ceteris paribus, I would prefer a non-sensical phrase composed of three valid words to a non-sensical phrase composed of three invalid words.  

There has been quite a discussion on the word 'poxleber' in the old forum

...and here in the You are not allowed to view links. Register or Login to view. thread as well. But I think Koen now really puts it in a different light from the linguistic point of view.