懐旧[kaikyuu] recalling the old days
旧ソ連[kyuusoren] former Soviet Union
旧悪[kyuuaku] past misdeeds
旧衣[kyuui] worn-out clothes
旧詠[kyuuei] ancient poems

旧怨[kyuuen] old grudge
旧縁[kyuuen] old relationship
旧恩[kyuuon] old favors
旧仮名遣[kyuukanazukai] former (i.e. before the post-WWII reforms) kana usage in writing the readings of kanji

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