Reduces speed in a gradual approach to central Ruislip (5)

I believe the answer is:

slows

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'reduces speed' is the definition.
(I've seen this in another clue)

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

(Other definitions for slows that I've seen before include "Decelerates" , "Retards" .)

I've seen this clue in the Evening Standard.

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