The most common and most likely answer to this crossword clue is the 10 letter word SACRAMENTS
I've seen this crossword clue in The Guardian
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Buddy explains!
The straight part
We know that "religious ceremonies" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case religious ceremonies = sacraments.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 SACRAMENTS mean?
SACRAMENTS noun- A sacred act or ceremony in Christianity. In Catholic theology, a sacrament is defined as "an outward sign instituted by Christ to give grace."
- (in particular) The Eucharist.
- The consecrated Eucharist (especially the bread).
- A thing which is regarded as possessing a sacred character or mysterious significance.
- The oath of allegiance taken by soldiers in Ancient Rome; hence, any sacred ceremony used to impress an obligation; a solemn oath-taking; an oath.