The most common and most likely answer to this crossword clue is the 9 letter word BOURGEOIS
I've seen this crossword clue in Independent
B
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More clues leading to the result BOURGEOIS
Buddy explains!

The straight part
We know that "middle-class" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case middle-class = bourgeois.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 BOURGEOIS mean?
BOURGEOIS noun- (usually in the plural) The middle class.
- An individual member of the middle class.
- (usually derogatory) A person of any class with bourgeois (i.e., overly conventional and materialistic) values and attitudes.
- (history) An individual member of the bourgeoisie, the third estate of the French Ancien Regime.
- A capitalist, (usually derogatory) an exploiter of the proletariat.
- To make bourgeois.
- Of or relating to the middle class, their presumed overly conventional, conservative, and materialistic values.
- Of or relating to the bourgeoisie, the third estate of the French Ancien Regime.
- Of or relating to the capitalist class, (usually derogatory) the capitalist exploitation of the proletariat.
- A size of type between brevier and long primer, standardized as 9-point.