The most common and most likely answer to this crossword clue is the 8 letter word OCTETTES
I've seen this crossword clue in Financial Times
O
C
T
E
T
T
E
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 = octettes.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 OCTETTES mean?
OCTETTES noun- A group or set of eight of something.
- A group of eight musicians performing together.
- A composition for such a group of musicians.
- A byte of eight bits. Abbreviation: o
- A group of three bits, representing any of eight possible values.