Afterwards put a trainee on edge (7)
I believe the answer is:
lateral
'edge' is the definition.
(thesaurus)
'afterwards put a trainee' is the wordplay.
'afterwards' becomes 'later' (synonyms).
'put' says to put letters next to each other.
'trainee' becomes 'l' (as in an L-plate for a learner driver).
'later'+'a'+'l'='LATERAL'
'on' acts as a link.
(Other definitions for lateral that I've seen before include "Sort of thinking" , "Sideways, like creative thinking" , "Relating to the side" , "Towards the side" , "This kind of sideways thinking does not use conventional logic" .)