Nazi secret police (7)
I believe the answer is:
gestapo
'nazi secret police' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for gestapo that I've seen before include "war force" , "Geheime Staatspolizei" , "Brutal force" , "Men in black" , "Postage for Hitler's police" .)