Arsenal initially sweeping away (6)
I believe the answer is:
abroad
'away' is the definition.
(I've seen this before)
'arsenal initially sweeping' is the wordplay.
'initially' says to take the initial letters.
'sweeping' becomes 'broad' (similar in meaning).
The first letter of 'arsenal' is 'a'.
'a'+'broad'='ABROAD'
(Other definitions for abroad that I've seen before include "out of UK?" , "in France, say" , "At large; widely current" , "Out of doors - in foreign parts" , "on the Continent" .)