Crossword Genius

Drilling ordeal possibly carnal too? (4,5,7)

Ross

I believe the answer is:

root canal surgery

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

'drilling' is the definition.
Both the answer and definition are singular nouns.
Maybe you can see a link between them that I don't see?

I cannot understand how the rest of the clue works.

Can you help me to learn more?

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