Groom has time for equestrian event (8)
I believe the answer is:
dressage
'equestrian event' is the definition.
(I've seen this before)
'groom has time' is the wordplay.
'groom' becomes 'dress' (synonyms).
'has' says to put letters next to each other.
'time' becomes 'age' (an age is a period of time).
'dress'+'age'='DRESSAGE'
'for' is the link.
(Other definitions for dressage that I've seen before include "The training of a horse in manoeuvres" , "Art of horse training" , "Part of equestrian event" , "Method of horse training" , "Training of a horse in deportment" .)