Crossword Genius

Did it contribute to the snarling of the old-time traffic? (7)

Ross

I believe the answer is:

growler

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'traffic?' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for growler that I've seen before include "Unfriendly dog" , "Iceberg" , "Perhaps bear" , "Dog perhaps" .)

I've seen this clue in the Evening Standard.
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