The most common and most likely answer to this crossword clue is the 9 letter word THREESOME
I've seen this crossword clue in The Guardian
T
H
R
E
E
S
O
M
E
More clues leading to the result THREESOME
- Little maids from school possibly see mother coming out
- Group meets hero unexpectedly
- . Motherese discombobulated triplets
- Trinity Hall, reading electrical engineering, student starts delving into book
- Company, they say, with problem, so it’s said: Freeman Hardy Willis, say
- Sex situation in which gooseberry gets to play a part?
- Article about doctor and prophet backing a small group
- Heroes met surprisingly small group
- See mother struggling
- See mother juggling triplets, perhaps?
Buddy explains!

The straight part
We know that "small group /small group" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case small group /small group = threesome.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 THREESOME mean?
THREESOME noun- A group of three people or things.
- An instance of sexual activity involving three people.