Crossword Genius

One having frightful ups and downs? (6-7)

Ross

I believe the answer is:

roller-coaster

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'one having frightful ups and downs?' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.

This is the entire clue.

Can you help me to learn more?

(Another definition for roller-coaster that I've seen is " Fairground ride".)

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