A binding agreement concluded by subjects of international law, namely states and international organizations.
"The two nations signed a treaty to establish mutual defense against future aggression."
In plain English: A treaty is an official agreement between two countries that they both promise to follow.
"The new treaty ended years of conflict between the two countries."
Usage: A treaty refers specifically to formal agreements between nations or international organizations rather than casual deals between individuals. Use this term when discussing legally binding diplomatic accords that govern relations across borders.
The word "treaty" comes from the Middle English trete, which was borrowed from Anglo-Norman and Old French. Originally, it referred to bargaining, negotiation, or an agreement between rulers and states.