I'm not an English major, but that sounds to me like contextual. That is to say, something external (in this case, to the subject) is having an influence on meaning - that is definition context.
On the other hand, (again, IMO) metatextual refers to self-referential meaning. If I used psychology to analyze psychology, that seems to be more metatextual. You're using the terms to define the terms, of sorts. Alternatively, I think it can be general parlance which defines further conversation about the meaning of the term.
I think it's important to note that meta-textual is not a word, according to Webster. Metafiction is given as an alternative - fiction that refers to writing fiction.