If we were to take the strongest definition of the word "reverend," it would be wrong to address any man in this way. Reverend, according to Webster's Dictionary, means, "to be worthy of reverence."
Reverence means, "to have a feeling or attitude of deep respect, love and awe, as for something sacred." We should respect and love men of God, but we should never look at them as being sacred. Only God should be revered.
I don't believe most people use this word in its truest sense, but they simply use it as a term of respect. It's a custom of our culture and should not be a point of contention.
I also would like to compliment you on your research of the word "reverend." As you said, this word can only be found one time in the Bible.
He sent redemption unto his people: he hath commanded his covenant for ever: holy and reverend is his name (Ps. 111:9).
God's name is holy and reverend; it is worthy of respect and awe. You might be interested in the Hebrew word translated as reverend in this verse. It is the Hebrew word "Yare." It means "to fear and or reverend."
It is used three hundred and fifteen times in the Old Testament. It is only translated as reverend once. It is primarily translated as the English words "fear" and "afraid."
In conclusion, notice how it's used in this Scripture: "O fear the LORD, ye his saints: for there is no want to them that fear him" (Ps. 34:9).
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