The most common and most likely answer to this crossword clue is the 3 plus 3 plus 7 letter word OLD BOY NETWORK
I've seen this crossword clue in The Guardian
O
L
D
B
O
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O
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K
More clues leading to the result OLD BOY NETWORK
- What a school like Eton has, covered in cobwebs?
- New blood initially transfused into busy New York coterie
- Corrupt world OK by Eton — it’s how Etonians thrive!
- Nobody let off Labour association
- Informal association let nobody supply labour
- New York bold to break seniors' complex
- Moving to New York — bold people form an influential group
- Bloody fantastic job! How did you get it?
Buddy explains!
The straight part
We know that "it’s how Etonians thrive" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case it’s how etonians thrive = old boy network.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.