Yeah, one big argument I had with my wife was the definition of "cheating." She said that swinging was cheating. I could not understand how she could see that and she could not understand how I could see it as not cheating.
So for awhile, we talked two different languages. It was frustrating. She was not placing a specific bad judgement on swinging. But after awhile, she did see that someone in an open marriage can lie to their partner and "really cheat." So we went for awhile when my "cheating" meant "really cheat" to her. Now, i think we have settled more on the poly view of this term.
I think in a sense, a lot of the poly vs mono arguments will go this way because polyamory group has put a lot of effort into thinking about such concepts whereas the monoculture just inherited the words. For example, in mono culture, jealousy is treated at the symptom level where the insecurity itself is treated in the poly community. There are some mono people who buy polyamory books just for concepts like this.
But there may be some mono/poly concepts/words that are no so clear cut like "marriage". And there is a lot of word definitions in the poly community that still have not been sorted out. I think the important thing is to talk about definitions with your partners. Get that clear first.
Oh, and another tough word to define is "sex." I think people need to clarify what they mean when they use it in a relationship. Once you hear, "We didn't have sex; I just gave him a blowjob" and then you are already dealing with an issue that could have been avoided.