staple

1. (now historical) A town containing merchants who have exclusive right, under royal authority, to purchase or produce certain goods for export; also, the body of such merchants seen as a group.Examples: "The customs of Alexandria were very great, it having been the staple of the Indian trade."; "For the increase of trade and the encouragement of the worthy burgesses of Woodstock, her majesty was minded to erect the town into a staple for wool."; "Calais was one of the ‘principal treasures’ of the crown, of both strategic and economic importance. It was home to the staple, the crown-controlled marketplace for England's lucrative textile trade, whose substantial customs and tax revenues flooded into Henry's coffers."countablehistoricaluncountable

2. (by extension) Place of supply; source.Examples: "Whitehall naturally became the chief staple of news. Whenever there was a rumour that anything important had happened or was about to happen, people hastened thither to obtain intelligence from the fountain head."broadlycountableuncountable