Employed American editor (4)
I believe the answer is:
used
'employed' is the definition.
('use' can be a synonym of 'employ')
'american editor' is the wordplay.
'american' becomes 'us'.
'editor' becomes 'ed'.
'us'+'ed'='USED'
(Other definitions for used that I've seen before include "Accustomed, having been put into service" , "was milking" , "cast off" , "Second hand" , "taken advantage of!" .)