The question comes out of an thought experiment which goes like this:
This is a first-rate question, if a little complicated, and deserves a longer (first-rate) answer. But it's Thanksgiving so I have to be brief! First your point about the dictionary is quite fascinating. I'm pretty sure Wittgenstein (and maybe Augustine) made roughly similar or closely related observations -- but partly in service of recognizing that ultimately for language/meaning to work we must connect (some) words not merely to other words but to 'reality' (or at least our perceptions thereof) -- we have some 'ostensive' definitions whereby we assign the meaning of a word by relating it directly to some object or object of perception ... (Not that that is problem-free itself, but it attempts to break the cycle of words-words definitions). Second, I'm not entirely clear on the analogy you make between the definition case and that of physical laws (and not clear whether the point I just made about ostensive definitions would apply in some analogous way to the laws). But apart from the analogy I can say you also have your finger on a very deep issue about explanation etc. -- and one response might be to point out that while perhaps we can explain various particular events by reference to the physical laws constitutiong the framework, that general strategy won't explain the laws themselves -- that at some point explanation of the system itself requires going outside the system (perhaps there's the analogy to ostensive definition) -- I think the great medieval thinker Maimonides made a point similar to this -- ultimately using it either as part of an argument to believe in the existence of God (as something outside the physical system that could explain the physical system), or at least to recognize that you can't apply the normal model of explanation of normal events back to explain the 'beginning' of the universe, creation ex nihilo .... Does this mean a 'theory of everything' isn't possible? Well, of course, better ask the physicists that. Pretty clearly such a theory would also have to explain itself ... (or else perhaps could a Theory of Everything include God etc.)? .... Anyway much more to say here, but many deep points are raised in your question ....
hope this is useful!