Approaches from one arsenal (5)
I believe the answer is:
nears
'approaches' is the definition.
('near' can be a synonym of 'approach')
'from one arsenal' is the wordplay.
'from' indicates the answer is hidden within the clue.
'NEARS' can be found hidden inside 'one arsenal'.
(Other definitions for nears that I've seen before include "Becomes closer" , "Comes closer" , "Gets closer" , "Bears down" , "Saner (anag.)" .)