Policeman's hot coming out of helicopter (6)
I believe the answer is:
copper
'policeman's' is the definition.
(copper can informally mean a police officer)
'hot coming out of helicopter' is the wordplay.
'hot' becomes 'h' (abbreviation, eg on taps).
'coming out of' indicates named letters should be taken away.
'helicopter' becomes 'chopper' (synonyms).
'chopper' with 'h' taken out is 'COPPER'.
(Other definitions for copper that I've seen before include "Small loose change" , "Ductile metal" , "Old policeman or reddish metal" , "Reddish metal of a penny" , "old tub" .)