|"borogove mimsy"="borogóv mimzi"|
OR, if you insist on vowel length (borogove=borogóv):
which leaves us with:
= boro miz or boró miz
z > r (rhotacism)
BUT. "Mimsy Borogoves" are nonsense words. "Boromir" has been given a meaning: 'faithful jewel' (source Tolkienwiki > search > Boromir).
If Lewis Carroll indulged in non-sense syllables, Tolkien indulged even more (since his elven glossary entries, even in just one of the major languages, probably by far outnumber the crypto-English glossary that could be made from The Hunting of the Snark*) in giving sense to his syllables.
Let us presume, I did not look up the meanings of the roots, it is boro that means faithful and mir that means jewel. I would not let mimsy mean faithful, and I hesitate to call things generally as small as jewels borogoves. So if this is where Tolkien came up with Boromir, he let adjective become noun and noun adjective. But the point is: there is something about "mimsy" which is repugnant to making it mean "faithful", there is nothing repugnant in making "mir" mean "jewel", there is something repugnant in making "borogove" mean "jewel", except a very big and costly such (thrones, crowns, scepters, Arkenstone - possibly, rings - no), there is nothing repugnant in making "boro" mean "faithful". Which is a point against the total arbitrariness of the relation of sound and meaning.
Paris IV - G. Pompidou
8/21 august A. D. 2009
*oops, that may be Jabberwocky I was thinking about!
OTHER UPDATE: the deletion rules above are what might have been contributing consciously or unconsciously to the invention of either name Boromir or elements it was made of in Tolkien's life, and are of course no more soundlaws for Quenya or Sindarin than cow > woc, how > hoc are internal soundlaws of Nevbosh.