Administrative Officer concealed a couple of grand? This could be explosive (4)
I believe the answer is:
ammo
'this could be explosive' is the definition.
The definition suggests a singular noun which matches the answer.
'administrative officer concealed a couple of grand?' is the wordplay.
'administrative officer' becomes 'ao' (this might be a standard abbreviation which I don't know about).
'concealed' indicates putting letters inside.
'a couple of' indicates the doubling of some letters.
'grand?' becomes 'M' ('M' can be a synonym of 'grand').
'm' doubled is 'mm'.
'ao' enclosing 'mm' is 'AMMO'.
Can you help me to learn more?
(Other definitions for ammo that I've seen before include "Bullets, shells, etc. (abbr.)" , "Bullets and bombs, etc (abbr)" , "explosives, perhaps" , "What's fired from a gun (abbr)" , "round" .)