Employed American boy (4)
I believe the answer is:
used
'employed' is the definition.
('use' can be a synonym of 'employ')
'american boy' is the wordplay.
'american' becomes 'US' (United States).
'boy' becomes 'ed' (short for Edward).
'us'+'ed'='USED'
(Other definitions for used that I've seen before include "Pre-loved" , "Sued (anag.)" , "with a previous owner" , "Was treating" , "Dues (anag.)" .)