Correct spelling, explanation: reverend is both a noun and an adjective. It was borrowed from Middle French révérend, from Old French, and from the Latin future passive participle reverendus (that is to be respected). As we can see, all the previous forms were spelled with only one vowel: -e. There is no place in this word for -a vowel. You can’t change any letters in a borrowing. Therefore, reverand is an incorrect form and the correct one is: reverend.

Definition of reverend:
1. noun, a member of the clergy
Reverend gave us his sermon and everyone thought it was very educational.
Reverend Smith has moved to a new church lately.
2. adjective, used as a title or form of address to members of the clergy
Reverend Mother is a woman who is the head of a convent.
I have to ask The Reverend Father if I can leave the monastery.

Collocations with reverend:
Some most commonly used collocations include: Reverend + name
Reverent Jones was on his way to Rome.
Reverend Ward is really kind: he always helps the homeless.

Incorrect spelling, explanation: there’s no reason why anyone would spell this word with -and instead of -end. The correct version, reverend, is a borrowing and it comes from Middle French. We must pay attention to the original spelling, which contains three -e vowels. Try to remember that only one vowel appears in this noun/adjective. Reverand doesn’t exist in any dictionary.