• 同盟どうめい — alliance
• 連盟れんめい — league; federation
• 加盟かめい — participation (in a league)
• 盟友めいゆう — ally; trusted partner
• 盟主めいしゅ — leader of an alliance
• 盟約めいやく — covenant; pledge

盟 combines 明 (bright/clear) and 皿 (dish/vessel), originally linked to rituals where an oath was sworn with offerings. It symbolizes a clear pledge or alliance made in front of others or the gods.

Today, it broadly refers to alliances, federations, and formal pledges among people or nations.

二国にこくは 同盟どうめいを 結むすんだ。
The two countries formed an alliance.

彼かれは 長年ながねんの 盟友めいゆうだ。
He is a longtime ally.