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

共棲[tomoiki] symbiosis
棲家[sumika] dwelling
水棲[suisei] aquatic (life)
棲息[seisoku] inhabiting
同棲[dousei] cohabitation

両棲[ryousei] amphibious
隠棲[insei] secluded life
旧棲[kyuusei] old home
棲み分け[sumiwake] habitat isolation (biology)
両棲動物[ryouseidoubutsu] amphibious animal