happening between more than two parties 英語で:

Multilateral trade negotiations ran aground over import quotas.

The countries have just signed a new multilateral convention.

multilateral /ˌmʌltiˈlætərəl; US / adj. involving more than two groups of people, countries, etc. They signed a multilateral agreement. ▶ wielostronny

Seven countries are taking part in the multilateral talks. The party leader has actually declared her support for unilateral nuclear disarmament (= giving up her country's nuclear weapons without first waiting for other countries to do the same).