Chief editor backing Arsenal (5)
I believe the answer is:
depot
'arsenal' is the definition.
(thesaurus)
'chief editor backing' is the wordplay.
'chief' becomes 'top' (synonyms).
'editor' becomes 'ed'.
'backing' is a reversal indicator.
'top'+'ed'='toped'
'toped' backwards is 'DEPOT'.
(Other definitions for depot that I've seen before include "Headquarters - storehouse" , "Storage base" , "Store for large quantities" , "Terminus for transport vehicles" , "Storage location" .)