A word class that is fairly common in European languages, and undoubtedly elsewhere as well, is the conjunction. Here, of course, a small warning is justified: 'and' as a word is less common cross-linguistically than you'd think.
Let's consider a language with rather little in ways of nominal marking: no case, or potentially very ambiguous case.
An example of the latter could be a language with GenN and SO order, where the possessum is marked by the same case as the object. Coordination ('and') would basically be dealt with by parataxis: "this that" → this and that.
Now, sometimes you may have things that are lined up in a way that looks very much like they belong to a GenN or an SO line-up, and one or the other might seem more like the 'reasonable' interpretation. In this case, a 'disjunction' could be introduced to mark that the two are not part of the same NP, or in the case of two nouns of the same marking next to each other, the disjunction could mark that they do not form a coordinated structure - an example for this would be a possessed noun and an object.
This might well be called a 'conjunction', but somehow it seems to behave syntactically in a way quite dissimilar from a conjunction.
I bet something along these lines does exist in some languages, and I would be happy to see comments if anyone knows of it!