The most common and most likely answer to this crossword clue is the 9 letter word SPINSTERS
I've seen this crossword clue in The Guardian
S
P
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More clues leading to the result SPINSTERS
Buddy explains!

The straight part
We know that "Unmarried ladies" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case unmarried ladies = spinsters.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 SPINSTERS mean?
SPINSTERS noun- (sometimes derogatory) A woman who has never been married, especially one past the typical marrying age according to social traditions.
- One who spins (puts a spin on) a political media story so as to give something a favorable or advantageous appearance; a spin doctor, spin merchant or spin master.
- Someone whose occupation was spinning thread.
- A woman of evil life and character; so called from being forced to spin in a house of correction.
- A spider; an insect (such as a silkworm) which spins thread.