Crossword Genius

One may go downhill fast (5)

Ross

I believe the answer is:

skier

I'm a little stuck... Click here to teach me more about this clue!

This clue could be a double definition.

'one may go downhill' is the first definition.
(I've seen this in another clue)

'fast' is the second definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.

Can you help me to learn more?

(Other definitions for skier that I've seen before include "One up mountain, perhaps" , "One on the piste" , "Winter sportsman" , "Winter sports person" , "He glides over snow, perhaps in sport" .)

I've seen this clue in The Sun.
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