What makes perfect business for a doctor (8)

I believe the answer is:

practice

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'what makes perfect' is the definition.
(I've seen this before)

I don't understand the remainder of the clue.

(Other definitions for practice that I've seen before include "''. . . . . . . . maked perfect''" , "training" , "Habit - procedure" , "Learn by repetition" , "The exercise of a profession" .)

I've seen this clue in The Times.

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