How to parse 'in as much' and similar syntagmas?

Question

[OED] inasmuch {adverb} = [Etymology:]
originally 3 words in as much (in northern Middle English in als mikel), subsequently sometimes written as 2 words, in asmuch, and now (especially since 17th cent.) as one.

I. In phrase inasmuch AS. [=] In so far as, [...], in proportion as,

†3. in as much (Notice the absence of as)
= [4.] In an equal or like degree, likewise.

[Beware: Only definition I contains the 4th AS; definition 3 lacks it.]

I already understand and so ask NOT about the definitions 1 and 3 above. Instead, I ask for a linguistic analysis of inasmuch (and similar syntagmas).
To parse it, I consider its original form as 3 separate words (in as much), as stated above.

1. In in as much, what do the 3 separate words mean individually?
For each of the 3 words, which definition from OED matches?
OED is linked here for your convenience: in, as, much.

2. How did the bolded 3 morphemes combine to mean definition 4? For example, 3 contains no word that means degree in definition 4. So whence did degree originate?

Please expose and explain all hidden, missing semantic drifts.

Answer 1

You won't clarify the expression "inasmuch as" by parsing. It is an idiomatic word formation and a conjunction and the only way to clarify is to show how the word elements, in, as, much, as can develop the special sense. A similar formation is insofar as, which has a parallel in German "insofern als".