Profession in which people are sure to take an interest (12)

I believe the answer is:

moneylending

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

'profession' is the definition.
The definition and answer are not the same part of speech.

'in which people are sure to take an interest' is the wordplay.
I cannot really see how this works, but
'in' is found in the answer.
'an' could be 'one' and 'one' is present in the answer.
This explanation may well be incorrect...

Can you help me to learn more?

(Another definition for moneylending that I've seen is " Charging of interest on advances".)

I've seen this clue in The Globe and Mail.

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