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

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adj. Of or relating to the preservation of peace, especially the supervision by international forces of a truce between hostile nations.

n. An effort to preserve peace between hostile groups, especially by a sanctioned military force.

adj. of or relating to the preservation of peace between hostile groups by international military forces

n. the activity of keeping the peace by military forces (especially when international military forces enforce a truce between hostile groups or nations)

"In the Mexican border city of Ciudad Juarez, business leaders are so concerned about spiraling drug cartel-related violence that they have asked the United Nations to send in peacekeeping soldiers to restore calm."

operation    military operation   

peacekeeper   

u.s.-led    host-nation    expeditionary    multinational    paramilitary