Crossword Genius

If you say “Whoa!” will it stop biting? (8)

Ross

I believe the answer is:

horsefly

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'it stop biting?' is the definition.
The definition suggests a singular noun which matches the answer.

I can't explain the rest of the clue.

Can you help me to learn more?

(Another definition for horsefly that I've seen is " sucker".)

I've seen this clue in the Evening Standard.
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