Crossword Genius

Operating on? (5)

Ross

I believe the answer is:

using

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'operating' is the definition.
(I've seen this in another clue)

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for using that I've seen before include "having recourse to" , "Putting to a particular purpose" , "Exercising" , "addiction" , "practice" .)

I've seen this clue in the Sydney Morning Herald.
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