What's wrong with the eligible bachelor? (5)

I believe the answer is:

catch

I'm a little stuck... Click here to teach me more about this clue!

'bachelor?' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for catch that I've seen before include "Concealed difficulty" , "Arrest" , "Hear < hit" , "Trap - hear - contract" , "Good match" .)

I've seen this clue in the Evening Standard.

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