Do individuals have an Occam’s razor for word meanings?

Semantics (and to a certain extent cognitive or even social psychology) studies the sort of thing you're after. But nobody (I know of) would formulate the problem in this way. An ancient school of Buddhist semantics (the name of which eludes me) postulated that the meaning of a word was everything that it wasn't.

However, the whole idea of meaning being the kind of definition that you would find in the dictionary has been completely rejected by many in semantics. It's still a useful shortcut to say things like 'a word means something' or 'a word has a meaning' but nobody would think of meaning as an unproblematic thing, any more.

Meaning is best described as a process which has a linguistic, cognitive (psychological) and social dimension. Words and phrases trigger certain ideas, images, frames, etc. which blend with others as well as the context. The way this happens depends on the language, the speakers knowledge and also the shared knowledge of a community.

So in effect, we don't have a personal definition of a word in our head. We have a complex network of uses, images, propositions, etc. associated with the word. A definition such as the one you listed is simply another way of using the word in context. It is a product of social interaction and an expression of our metacognitive ability (ability to reflect on our speech and cognition), not the actual meaning or a description of that meaning.

From a linguistic perspective, it is important to think of dictionaries as just another text (albeit one with metalinguistic aims) and not a template for some sort of a mental lexicon. That does not mean a dictionaries or word definitions are not useful (or even indispensable tools). They are. But they must not be confused for anything more fundamental than that.