They signed a treaty to lower duties on trade between their countries.
source: WordNet 3.0
A schedule, system, or scheme of duties imposed by the government of a country upon goods imported or exported; as, a revenue tariff; a protective tariff; Clay's compromise tariff. (U. S. 1833).
source: Webster 1913
A tariff may be imposed solely for, and with reference to, the production of revenue (called a revenue tariff, or tariff for revenue, or for the artificial fostering of home industries (a projective tariff), or as a means of coercing foreign governments, as in case of retaliatory tariff.