Here’s the thing. I don’t actually like the definition of the word “microtonal.” Well, I’m sure I’m not the only one.
It’s always tricky having a word which is defined by which it is not. And microtonal means any music that uses intervals smaller (or larger) than a Western equal-tempered semitone. Essentially, we can take microtonal to mean any music or scale that isn’t 12-tone equal temperament. This just elevates 12-tet to something much bigger than it really is.
Many microtonalists I talk to these days see the tuning space as containing an infinite number of tunings; 12-tone equal temperament being just another one of them. But the word we use to describe this tuning space really only includes all of those tunings but one (12-edo). Why the disconnect between the definition and the reality?
“Xenharmonic” suffers the same problem. This word means any music that sounds different to 12-tone equal temperament. (Let’s just put aside the slippery problem of what sounds different today becomes familiar tomorrow).
I would prefer xenharmonic to mean: music that sounds different to ANY traditional music (not just Western music). For example, I wouldn’t class maqam music as xenharmonic, because it’s a traditional music. This seems a more useful distinction to make and it removes the cultural bias currently present in the term.
I know that others will disagree, and that’s just fine. Languages and cultures shift all the time.