Boy comes up on track, not taking a breather (7)

I believe the answer is:

nostril

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'breather' is the definition.
(I've seen this before)

I don't understand the remainder of the clue.

(Other definitions for nostril that I've seen before include "Through which one would snort" , "Nose hole" , "Breathing space" , "Aperture in nose" , "Breathing aperture" .)

I've seen this clue in The Times.

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