The most common and most likely answer to this crossword clue is the 5 letter word ABUNA
A
B
U
N
A
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The straight part
We know that "head of church" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case head of church = abuna.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does ABUNA mean?
ABUNA noun- The Patriarch, or head of the Abyssinian Church.