The most common and most likely answer to this crossword clue is the 12 letter word PROCESSIONAL
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More clues leading to the result PROCESSIONAL
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The straight part
We know that "moving hymn" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case moving hymn = processional.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.
Crossword Answer definitions
PROCESSIONAL noun- A hymn or other music used during a procession; prosodion.
- A group of people or things moving along in an orderly, stately, or solemn manner.
- A service book relating to ecclesiastical processions.
- Of, pertaining to, or used during a procession, particularly at the start of a religious ceremony or wedding.