It's used to clear a bottleneck (9)

I believe the answer is:

corkscrew

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'bottleneck' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.

I can't explain the rest of the clue.

Can you help me to learn more?

(Other definitions for corkscrew that I've seen before include "Spiral device for wine lovers" , "Graves opened by this" , "convoluted course" , "Wine bottle opener" , "Bordeaux might require this?" .)

I've seen this clue in The Globe and Mail.

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