契り[chigiri] pledge
契る[chigiru] to pledge
契印[keiin] impression of a seal over the joint of two papers
契機[keiki] opportunity
契約[keiyaku] contract

契約期間[keiyakukikan] contract period
契約書[keiyakusho] (written) contract
信託契約[shintakukeiyaku] trust agreement
双務契約[soumukeiyaku] bilateral agreement
二世の契り[nisenochigiri] marriage vows

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