staple
nounA settled mart or market; an emporium. In England, formerly, the kings staple was established in certain ports or towns, and certain goods could not be exported, without being first brought to these ports to be rated and charged with the duty payable to the king or public. The principal commodities on which customs were levied, were wool, skins and lether, and these were originally the staple commodities. Hence the words staple commodities, came in time to signify the principal commodities produced by a country for exportation or use. Thus cotton is the staple commodity of South Carolina, Georgia and other southern states of America. Wheat is the staple of Pennsylvania and New York.