The most common and most likely answer to this crossword clue is the 17 letter word LADIES-IN-WAITING
I've seen this crossword clue in The Times
L
A
D
I
E
S
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I
N
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W
A
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T
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G
Buddy explains!

The straight part
We know that "g/retinue" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case g/retinue = ladies-in-waiting.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 LADIES-IN-WAITING mean?
LADIES-IN-WAITING noun- A lady, often a noblewoman, in the household of a queen, princess, or other woman of higher rank who attends her as a personal assistant, generally a role considered an honour.