This section is from the "A Complete Dictionary of Dry Goods" book, by George S. Cole. Also available from Amazon: A complete dictionary of dry goods and history of silk, cotton, linen, wool and other fibrous substances,: Including a full explanation of the modern processes ... together with various useful tables.
Tariff. A term derived from Tarifa, Spain. This town received its name from Tarifa Malek, a Saracen chief, who landed at that point on the coast in 710, and during the Moorish domination all vessels which passed through the Straits of Gibralter were at Tarifa compelled to pay duties or tribute to the savage chief; whence the word "tariff." As used at present, the word indicates a list of goods, with the specified duties or customs to be paid for the same, either on importation or exportation. In the United States there can be no duties imposed on exports; our tariff duties must all be laid on imports. Ad valorem is the duty, or tariff, on the net value of an invoice of goods. Advalorem duties are levied according to the market value or worth of goods at the original place of shipment, as sworn to by the owner and verified by the custom appraisers. Specific duty is the duty, or tariff, on the number or quantity, as dozens, gross, or tons. [See Imports, Appendix "C."]