The most common and most likely answer to this crossword clue is the 9 letter word NIGHTGOWN
I've seen this crossword clue in The Times
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I
G
H
T
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N
More clues leading to the result NIGHTGOWN
- Something worn for going out, good in nearby shopping centre
- Wrong thing for arousal — take right off!
- New wig and thong, kinky bedroom gear
- Black community on campus giving something to don for retirement
- Unusual thing: good to have this for one’sretirement?
- Retirement habit’s good in nearby urban area
- Late replacement for evening dress?
- Near an urban area covering source of gold that might do for retirement
- Loose robe dressing government leader in municipality just around the corner?
- Cover for the retired
Buddy explains!

The straight part
We know that "something to don for retirement" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case something to don for retirement = nightgown.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 NIGHTGOWN mean?
NIGHTGOWN noun- A long loose robe worn mainly by women for sleeping in.
- A dressing gown.