The most common and most likely answer to this crossword clue is the 9 letter word ENSEMBLES
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Buddy explains!
The straight part
We know that "Groups" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case groups = ensembles.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 ENSEMBLES mean?
ENSEMBLES noun- A group of separate things that contribute to a coordinated whole.
- A coordinated costume or outfit; a suit.
- (collective) A group of musicians, dancers, actors, etc who perform together; e.g. the chorus of a ballet company.
- A piece for several instrumentalists or vocalists.
- A probability distribution for the state of the system.
- (machine learning) A supervised learning algorithm combining multiple hypotheses.