The most common and most likely answer to this crossword clue is the 10 letter word BAPTISTERY
I've seen this crossword clue in Financial Times
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Buddy explains!
The straight part
We know that "Part of church" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case part of church = baptistery.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 BAPTISTERY mean?
BAPTISTERY noun- A designated space within a church, or a separate room or building associated with a church, where a baptismal font is located, and consequently, where the sacrament of Christian baptism (via aspersion or affusion) is performed.
- An indoor pool used for baptism by immersion.