The most common and most likely answer to this crossword clue is the 13 letter word ARCHIMANDRITE
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The straight part
We know that "who’s in charge of monastery?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case who’s in charge of monastery? = archimandrite.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 ARCHIMANDRITE mean?
ARCHIMANDRITE noun- The superior of a large monastery, or group of monasteries, in the Orthodox Church.
- An honorary title sometimes given to a monastic priest.