Two reasons why I pronounce it Hal-o-ween: It is a shortened way of saying All Hallows Eve (and is pronounced the same as in the first part of "Hallowed be Thy Name from the Lord's Prayer). Also, being the ever-ready school teacher, when you divide this word into syllables, you would divide the first part between the two Ls as in Hal-low-een. Either way, your wife is right. But I am sure that's a given!!