The Collaborative International Dictionary of English v.0.48:

Arsenal \Ar"se*nal\ ([aum]r"s[-e]*nal), n. [Sp. & F. arsenal
   arsenal, dockyard, or It. arzanale, arsenale (cf. It. &
   darsena dock); all fr. Ar. d[=a]r[,c]in[=a]'a house of
   industry or fabrication; d[=a]r house + [,c]in[=a]'a art,
   industry.]
   A public establishment for the storage, or for the
   manufacture and storage, of arms and all military equipments,
   whether for land or naval service.
   [1913 Webster]

WordNet (r) 3.0 (2006):

arsenal
    n 1: all the weapons and equipment that a country has [syn:
         arsenal, armory, armoury]
    2: a military structure where arms and ammunition and other
       military equipment are stored and training is given in the
       use of arms [syn: arsenal, armory, armoury]
    3: a place where arms are manufactured [syn: armory,
       armoury, arsenal]