The most common and most likely answer to this crossword clue is the 5 letter word TEAMS
I've seen this crossword clue in The Daily Telegraph
T
E
A
M
S
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 = teams.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 TEAMS mean?
TEAMS noun- A set of draught animals, such as two horses in front of a carriage.
- Any group of people involved in the same activity, especially sports or work.
- A group of animals moving together, especially young ducks.
- A royalty or privilege granted by royal charter to a lord of a manor, of having, keeping, and judging in his court, his bondmen, neifes, and villains, and their offspring, or suit, that is, goods and chattels, and appurtenances thereto.
- To form a group, as for sports or work.
- (by extension) To go together well; to harmonize.
- To convey or haul with a team.
- To form together into a team.
- To give work to a gang under a subcontractor.