Dog that races the bus? (9)

I believe the answer is:

greyhound

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'dog' is the definition.
(greyhound is a kind of dog)

I can't explain the remainder of the clue.

(Other definitions for greyhound that I've seen before include "Want to bet on it?" , "Fast-moving dog" , "Tall, slender canine" , "racer" , "Swift breed of dog" .)

I've seen this clue in The Sun.

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