Groom needs time for horse training (8)
I believe the answer is:
dressage
'training' is the definition.
(I know that training can be written as dressage)
'groom needs time' is the wordplay.
'groom' becomes 'dress' (synonyms).
'needs' means one lot of letters go next to another.
'time' becomes 'age' (an age is a period of time).
'dress'+'age'='DRESSAGE'
'for horse' acts as a link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for dressage that I've seen before include "equestrian routine" , "Art of horse training" , "Equestrian manoeuvres" , "Method of horse training" , "Art of training horses" .)