Along the wires the electric message came, a story from the Press Association: “Nuclear powers promise to eliminate their arsenals”, reporting the agreement by the 187 signatories to the Nuclear Non-proliferation Treaty (though the unspecific timescale reminded me of a wayside pulpit sign I once saw outside a chapel in Wales: “The promises of God are signed and sealed, but not dated”).
The word arsenal has a complicated history. It started in Arabic as dar-as-sina, meaning “house of industry” or “house of construction”. In the fifteenth century the word was taken over by several Mediterranean nations; both Spanish and Italian borrowed it as darsena, a word for a dock. The citizens of Venice acquired it in a different form, losing the first letter and adding al to the end, as the name of their naval dockyard, a substantial base as befitted the leading maritime power in the Mediterranean at the time; to this day it’s called the Arzenale.
The English may have got the word from French but it is more likely that it came directly from Venetian Italian, since early uses are in descriptions of the dockyard. For example, William Thomas wrote in a History of Italy in 1549 — definitely the book to read at the time if you wanted to know about the main Italian states: “The Arsenale in myne eye excedeth all the rest: For there they haue well neere two hundred galeys” (“In my eyes the Arsenale is greater than all the others; they have almost two hundred galleys there”).
Later in the sixteenth century the word’s meaning began to shift in English towards naming one part of a dockyard, a warehouse for naval stores and weapons; later still it referred specifically to a place of storage for weapons of all kinds, not just naval ones (a famous examples was the Federal arsenal at Harper’s Ferry which John Brown stormed in 1859) and also for a place where weapons were made and repaired. That remained its principal meaning in English until comparatively recently. A famous example was the Royal Arsenal on the Thames east of London, which stretched for a mile along the river next to the Woolwich dockyard, and which gave its name to the football club.
It was only a step further to use it for the whole collection of weapons and other military equipment available to a group or country, a meaning that appeared less than a century ago. Hence the phrase nuclear arsenal. It’s a long way from an Arabian factory.