Stable lad can be trained (8)
I believe the answer is:
balanced
'stable' is the definition.
('balanced' can be similar in meaning to 'stable')
'lad can be trained' is the wordplay.
'trained' indicates an anagram (to train can mean to grow something into a shape).
'lad'+'can'+'be'='ladcanbe'
'ladcanbe' anagrammed gives 'BALANCED'.
(Other definitions for balanced that I've seen before include "Auntie is supposedly" , "Stable - poised" , "Equitable" , "Composed - unbiased" , "Having weight equally distributed" .)