Soldier packing a small collection of weapons? (4)
I believe the answer is:
arms
'collection of weapons?' is the definition.
(arms can mean weapons)
'soldier packing a small' is the wordplay.
'soldier' becomes 'rm' (Royal Marine).
'packing' means one lot of letters goes inside another.
'small' becomes 's' (abbreviation - e.g. clothes size).
'a'+'s'='as'
'rm' put inside 'as' is 'ARMS'.
(Other definitions for arms that I've seen before include "What the Venus de Milo lacks" , "Protesting violently, up in these" , "Weapons and limbs" , "Guns et cetera" , "Ordnance" .)