Operator; addict (4)
I believe the answer is:
user
I believe this clue is a double definition.
'operator' is the first definition.
(I've seen this in another clue)
'addict' is the second definition.
(drug user)
(Other definitions for user that I've seen before include "One who employs" , "one has to employ" , "One taking drugs" , "One getting benefit from" , "Junkie's" .)