I first came across the term Metaclass around 1980 in the context of a programming language - Smalltalk, in fact. In dynamic OO programming languages like Smalltalk, CLOS, etc a Metaclass is a class whose instances are classes. That makes good sense to me.
Later, in the modelling world, some people started using Metaclass to mean "a class in a metamodel". This is much less justifiable. If your metamodel contains a class called UseCase, say, then instances of that class are objects that represent use cases. It makes much more sense to say that if my domain concerns use cases, then a class called UseCase is a domain class. That's why we call them DomainClasses in our framework.
A similar argument applies to DomainProperty - a property of a DomainClass. "Metaproperty" would mean something like "a property whose instances are properties".