Terrain reimagined for coach (7)
I believe the answer is:
trainer
'coach' is the definition.
(thesaurus)
'terrain reimagined' is the wordplay.
'reimagined' indicates an anagram.
'terrain' anagrammed gives 'TRAINER'.
'for' is the link.
(Other definitions for trainer that I've seen before include "Coach - one of a pair of shoes?" , "Terrain (anag.)" , "Coach; shoe" , "Comfortable shoe" , "one that helps runner perform" .)