Employer provides a course in the City (4)
I believe the answer is:
user
'employer' is the definition.
(thesaurus)
'a course in the city' is the wordplay.
'a course' becomes 'se'.
'in the' means one lot of letters goes inside another.
'city' becomes 'ur'.
'se' put inside 'ur' is 'USER'.
'provides' is the link.
(Other definitions for user that I've seen before include "One operating something" , "Junkie's" , "One who works an appliance" , "Operator; drug addict" , "Tech support caller?" .)