Sensible with the animal; a lion, trained (8)
I believe the answer is:
rational
'sensible' is the definition.
('rational' is associated in meaning with 'sensible')
'the animal a lion trained' is the wordplay.
'the animal' becomes 'rat' (rat is a kind of animal**).
'trained' indicates an anagram (to train can mean to grow something into a shape).
'a'+'lion'='alion'
'alion' with letters rearranged gives 'ional'.
'rat'+'ional'='RATIONAL'
'with' acts as a link.
(Other definitions for rational that I've seen before include "Consistent with logic" , "Based on logic or reasoning" , "Reasonable - sane" , "Requiring the use of the mind" , "Reasoning, logical" .)