I had always (60 years of playing) heard and seen the word spelled "embrouchure". When, recently, a friend spelled it as "embouchure", I almost was going to correct him. Instead, I looked it up on Wikipedia and other net sources and found that is is, in fact, the PREFERRED spelling. It is said that it is from the French (of course) for applying the mouth. (La bouche)
As a word junkie, I wonder if anyone has the derivation of the newer (incorrect?) spelling?