Simian trained a kelpie (7)
I believe the answer is:
apelike
'simian' is the definition.
(I've seen this before)
'trained a kelpie' is the wordplay.
'trained' is an anagram indicator (to train can mean to grow something into a shape).
'a'+'kelpie'='akelpie'
'akelpie' is an anagram of 'APELIKE'.
(Other definitions for apelike that I've seen before include "anthropoid" , "resembling some mammals" , "Simian" .)