This word is acceptable for play in the US & UK dictionaries that are being used in the following games:

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adj. Having many sides.

adj. Involving more than two nations or parties: multilateral trade agreements.

adj. Having many sides or points of view.

adj. Involving more than one party (often used in politics to refer to negotiations, talks, or proceedings involving several nations).

adj. Having many sides; many-sided.

In mathematics, having more lines or sides than one.

Hence Generally, many-sided.

adj. having many parts or sides

"Annan used the word multilateral nine times before mentioning Iraq."

four-sided    two-lobed    three-lobed    two-sided    quadripartite    two-part    four-party    triangular    three-way    two-way   

many-sided    many-side   

bilateral    collateral    lateral    plurilateral    trilateral    unilateral   

intergovernmental    nongovernmental    multinational    israeli-palestinian    bilateral    nonpartisan    unilateral    cross-border    faith-based    interfaith