When people are part of a subculture, they often create words that suit the needs of their various activities, feelings, or otherwise somewhat unique experiences. In polyamory, we have words like "frubble", "compersion", and "metamour" to describe some of the things that commonly used language has no single term for. In bdsm, there's top, bottom, switch, domme, sub and many more.
Within the poly community, terminology is something that is consistently debated. From hierarchical terms, like primary and secondary, to unicorns, pods, and fulcrums, and the term polyamory itself, these ideas are pulled apart, examined, put through the ringer, and, if enough people find them useful, they become part of the common lexicon. Common, at least within our little subculture...
Some question the use of "special" vocabulary. Doesn't it just continue to set us apart from society at large? Is it isolating? Is it silly to create words to suit our own needs? To me, it seem more ludicrous and clunky to say, "my partner's partner" than just metamour. It feels bulky and inefficient to use, "I feel joy in my partner's other relationships" instead of compersion. The language, as it stands, might have the words available to describe all of the same things, but it is more streamlined to have vocabulary that suits our needs, rather than stretching the current terminology to cover something that is outside its present bounds.
The idea that we are setting ourselves apart from larger society by using terminology that fits our life experience is disingenuous. We are setting ourselves apart from the mainstream by our actions! We use certain words to describe the actions, roles, and emotions that are common within our community. The words are not the differences themselves, and they don't make us a subculture by using them. "They might notice that we're not conforming if we have our own vocabulary. Shhhhh!" Like someone wouldn't pick out "My husband's girlfriend's husband's girlfriend." as a bit off the beaten path?!?!?!
"Well, I get tired of explaining what these poly-specific words mean to people." This sounds a lot like, "I only use words that are mainstream, so that I don't stand out." or "I only use short words that are easily understood, because explaining who I am is uncomfortable." Language is shorthand. It is a way to get a concept from one brain to another. Any specialized field has it's own vocabulary. No one thinks it's odd if someone who is tech saavy needs to explain cloud computing to someone who isn't familiar with the concept. Once it's been explained, it saves a lot of excess words in future conversations. In the same way, after sharing a definition for "metamour", your next conversation with your buddy about your dating life could be much less wordy.
Lastly, there are concepts that we have in poly, like compersion, that don't have easy equivalents in common usage. Words that have valuable ideas to share, ideas that could benefit society at large if they become more familiar. Holding those concepts close to our chest sets us apart. Not sharing our language diminishes the base values of openness and abundance that are at the core of what polyamory is. Let the terminology F L O W!