Semantic truth!
Rare or disfavored.
Perhaps-
"Unusual or frowned upon."
"Uncommon, yet accepted."
"Bigger than a breadbox, and smaller than a rhinoceros."
That wasn't the intent. Disfavored, as in disliked.
I was trying to give a scale, where:
(1) was no multiclassing (either due to preference, or rule); and
(2) was limited multiclassing, either because no one was doing it, or people weren't big fans of it for whatever reason.
Basically, though, it's a 1-5 scale.