I agree with CielDuMatin.
My problem with your view, capricorny, is that I just don't get it. It seems to me you are taking polyamory, then saying "if that one specific thing out of thousands of possible differences isn't like the way I do it, there should be a different word". I just don't see that.
I also think choosing a word that basically means the exact same thing, for a difference that isn't that obvious or necessitating a specific word for everyone, is confusing things even more. How are people supposed to remember which is which, when they sound pretty much the same are one is a subcategory of the other and, it seems to me, vague enough that it's not necessarily easy to tell which category does what.
It just seems to me like you're saying "my poly should be called poly, let's find a word for people who are different" and I don't really like that.
I see things pretty much like Ciel. You have relationships, among which romantic relationships (used in a broad way, to include sex without feeling. I mean relationships other than friendship and family), among which monogamy and non-monogamy, and within non-monogamy you have polyamory and swinging, and possibly both at once for some people.
It's complicated and confusing enough as it is, I feel.
At every level, there might be honesty, or there might not be. You might be cheating on your wife, that you don't love anymore, and she has no idea (which is the basis of cheating, I'd say). You might not love your wife anymore and have a relationship with someone else, and she's aware of it and okay with it.
In my opinion, that's not polyamory because you don't have a relationship with your wife anymore. You just say married for other reasons. Honesty and dishonesty are both possible.
Then with swinging, you can do it behind your partners back or have your partner know and be okay with it. There again, there is honesty or there isn't, and the non-honest way is called cheating.
With polyamory, there again, you can do it behind your partners back or have them know and be okay with it.
And in all of them, there is a middle-ground, where the partner knows, you know they know, but you don't talk about it and possibly pretend like nothing's happening. Happens in all three types of relationships. I don't think there should be a specific word for it just if it's in a polyamourous context and not for the other ones. I think, like cheating, you might want to find a word for it that applies to all cases, but I don't personally see it as absolutely necessary, since we have a word for the opposite: fidelity.
So we have cheating, fidelity, and that thing that's in the middle. And all three can apply to every type of non-monogamous relationship in similar ways.
In monogamous relationship, fidelity isn't exactly the same, since it means keeping the relationship monogamous, but still when you think about it, fidelity means having rules and following them, cheating means breaking the rules, and in the middle it's a kind of grey area where you're not breaking rules but that's because they don't exist, in a way.