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

悪習[akushuu] bad habit
悪習慣[akushuukan] bad habit
演習[enshuu] practice
演習問題[enshuumondai] practice problem
演奏練習[ensourenshuu] musical rehearsal

学習[gakushuu] study
学習者[gakushuusha] learner
学習塾[gakushuujuku] private night-school
学習用[gakushuuyou] tutorial
学習用ヘルプ[gakushuuyouherupu] tutorial help