The most common and most likely answer to this crossword clue is the 9 letter word SECESSION
I've seen this crossword clue in The Guardian
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More clues leading to the result SECESSION
- Financial centre in period of activity for Brexit, say
- Withdrawal from church in the course of meeting
- Breakaway meeting involving London’s financial district?
- Sitting outside church in withdrawn group
- Meeting welcoming European Community withdrawal
- Schism from church in conclave
- Austrian art movement’s formal separation
Buddy explains!

The straight part
We know that "Breakaway" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case breakaway = secession.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 SECESSION mean?
SECESSION noun- The act of seceding.