One little Correction: mur and mûr
I'm afraid I have to correct you in one little point:
You wrote: "meur (wall) became mûr where the preceding e was dropped."
But the wall - le mur is written without a circumflex.
mûr, mûre, however, is an adjective which means and stems from "mature", with the circumflex in memory of the -at- lost.