Right here, right now: Your use of "definition" is foreign to me. I do not have definitions of words in my head, but understandings or interpretations.

A definition is something that would be in a dictionary book.

Haha fair enough! I use definition to mean essentially "what one sees as the meaning of a word". That "one" could be Webster or another dictionary. Or an individual.

Your definition, is "the meaning of a word as specified in a dictionary".

There's definitely variance between these two definitions, but I think it's a small variance, and we can largely still understand each other despite the variance. I would say that word has converged on a meaning. We could, if we decided it was necessary, create separate words, one to mean an exact definition as defined by an authoritative source, and one to mean how every individual defines a word. But English society has decided that distinction isn't worth creating a new word at this time.

My argument is that introvert/extrovert have much more variance. When some people use the term, they use it to describe a behaviour, a temporary state, a constant personality trait, a spectrum, two perpendicular dimensions, a label on a loose set of behaviours, social skills, energy levels -- it's got so many facets! And dictionaries follow human usage -- so how is a dictionary supposed to pin this down to one or two concise definitions? That's my argument for why the terms are too variant to be exceptionally useful/meaningful.