A very exacting business (5)

I believe the answer is:

usury

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

'a very exacting business' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.

This is all the clue.

Can you help me to learn more?

(Other definitions for usury that I've seen before include "Demanding excessive interest" , "Money-lending at very high rates" , "Money-lending at exorbitant rates" , "Taking great interest" , "High-interest lending" .)

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

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.