The most common and most likely answer to this crossword clue is the 9 letter word LAYPERSON
I've seen this crossword clue in Financial Times
L
A
Y
P
E
R
S
O
N
Buddy explains!

The straight part
We know that "Parishioner" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case parishioner = layperson.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 LAYPERSON mean?
LAYPERSON noun- A person who is not a cleric.
- One who is not intimately familiar with a given subject or activity.