Crossword Genius

With which to reach Spooner’s distant county? (3-5)

Ross

I believe the answer is:

car-ferry

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'county?' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.

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

Can you help me to learn more?

(Another definition for car-ferry that I've seen is " Vehicle transporter".)

I've seen this clue in The Times.
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