加盟[kamei] participation
加盟国[kameikoku] member-nation
加盟者[kameisha] participants
加盟店[kameiten] participating store
軍事同盟[gunjidoumei] military alliance

三国同盟[sangokudoumei] triple alliance
盟う[chikau] to swear
同盟休校[doumeikyuukou] student strike
同盟軍[doumeigun] allied armies
同盟国[doumeikoku] ally (of another nation)

安全保障条約[anzenhoshoujouyaku] US-Japan Security Treaty
違約[iyaku] breach of contract
違約金[iyakukin] penalty for contract breach
一粒子既約[ichiryuushikiyaku] one particle irreducible (physics)
化学兵器禁止条約[kagakuheikikinshijouyaku] chemical weapons ban treaty

仮条約[karijouyaku] provisional treaty
会う約束[auyakusoku] rendezvous
会員規約[kaiinkiyaku] membership agreement (e.g. for a credit card)
解約[kaiyaku] cancellation of contract
確約[kakuyaku] firm promise