Government soldier in Engineers (6)
I believe the answer is:
regime
'government' is the definition.
('regime' can be a synonym of 'government')
'soldier in engineers' is the wordplay.
'soldier' becomes 'gi' (government issue or general issue).
'in' indicates putting letters inside.
'engineers' becomes 'reme' (I've seen this in other clues).
'gi' put into 'reme' is 'REGIME'.
(Other definitions for regime that I've seen before include "Method or system of government" , "Plan for therapy or government in power" , "Emigre (anag.)" , "co-ordinated programme" , "Ruling system" .)