The most common and most likely answer to this crossword clue is the 8 letter word SMASHING
I've seen this crossword clue in Financial Times
S
M
A
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H
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More clues leading to the result SMASHING
Buddy explains!
The straight part
We know that "Breaking up/wonderful" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case breaking up/wonderful = smashing.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 SMASHING mean?
SMASHING verb- To break (something brittle) violently.
- To be destroyed by being smashed.
- To hit extremely hard.
- To ruin completely and suddenly.
- To defeat overwhelmingly; to gain a comprehensive success.
- To deform through continuous pressure.
- To have sexual intercourse with.
- Gerund: The action of the verb to smash.
- Serving to smash (something).
- (originally United States, slightly obsolete) Wonderful, very good or impressive.