The most common and most likely answer to this crossword clue is the 9 letter word RELIQUARY
I've seen this crossword clue in The Times
R
E
L
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Q
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More clues leading to the result RELIQUARY
Buddy explains!
The straight part
We know that "Cathedral treasure" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case cathedral treasure = reliquary.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 RELIQUARY mean?
RELIQUARY noun- A container to hold or display religious relics.
- An object that sustains the memory of past people or events.
- A person who owes a balance.