Man retains work in aspiration (4)
I believe the answer is:
hope
'aspiration' is the definition.
(thesaurus)
'man retains work' is the wordplay.
'man' becomes 'he' (**).
'retains' indicates putting letters inside.
'work' becomes 'op' (abbreviation for opus).
'he' enclosing 'op' is 'HOPE'.
'in' acts as a link.
(Other definitions for hope that I've seen before include "Anticipation" , "Confident expectation" , "'. . . . springs eternal in the human breast'" , "Bob --, US comedian" , "writer" .)