The most common and most likely answer to this crossword clue is the 4 letter word SEPT
I've seen this crossword clue in The Times
S
E
P
T
More clues leading to the result SEPT
- Irish group's record set in stone
- One tribal division – but over half a dozen in France
- Short part of year for some Irish clan
- Clan that comes when summer turns to autumn
- Osteopath regularly visited clan
- Thirty days for family in Ireland extended
- Part of tribe quietly invading group
- Tribal group determined to seize power
Buddy explains!

The straight part
We know that "Irish group" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case irish group = sept.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 SEPT mean?
SEPT noun- A clan, tribe, or family, proceeding from a common progenitor (used especially of the ancient clans in Ireland).
- An enclosure; a railing.