Policeman takes heroin in helicopter (7)
I believe the answer is:
chopper
'helicopter' is the definition.
(synonyms)
'policeman takes heroin' is the wordplay.
'policeman' becomes 'copper' (copper can informally mean a police officer).
'takes' indicates putting letters inside.
'heroin' becomes 'H' (H is a slang term for heroin).
'copper' going around 'h' is 'CHOPPER'.
'in' is the link.
(Other definitions for chopper that I've seen before include "that's used by a lumberjack" , "An axe, or a slang helicopter" , "An informal helicopter, or an axe" , "Butcher's cleaver" , "Small axe" .)