The most common and most likely answer to this crossword clue is the 8 letter word ALDERMEN
I've seen this crossword clue in The Guardian
A
L
D
E
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M
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Buddy explains!

The straight part
We know that "Old councillors" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case old councillors = aldermen.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 ALDERMEN mean?
ALDERMEN noun- A member of a municipal legislative body in a city or town.
- A half-crown coin; its value, 30 pence.
- A long pipe for smoking.