Sound of equine expending energy nearby (4)

I believe the answer is:

nigh

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

I can't explain the remainder of the clue.

(Other definitions for nigh that I've seen before include "Old word for near, as the end may be" , "See 23" , "Near at hand" , "Near, as in archaic usage" , "old touch" .)

I've seen this clue in The Sun.

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