Work a long time on hill as a surgeon (8)
I believe the answer is:
operator
'a surgeon' is the definition.
(thesaurus)
'work a long time on hill' is the wordplay.
'work' becomes 'op' (abbreviation for opus).
'a long time' becomes 'era' (a long period of time).
'on' says to put letters next to each other.
'hill' becomes 'tor' (tor is a kind of hill).
'op'+'era'+'tor'='OPERATOR'
'as' is the link.
(Other definitions for operator that I've seen before include "Wheeler-dealer - telephonist" , "Manipulative type of person" , "Controller of machinery" , "Agent that runs some apparatus or machine" , "One using an item of equipment" .)