外壕[sotobori] outer moat (castle)
塹壕[zangou] trench
内壕[uchibori] inner moat
防空壕[boukuugou] air-raid shelter

掩壕[engou] cover trench
待避壕[taihigou] bomb shelter
塹壕熱[zangounetsu] trench fever

空オケ[karaoke] karaoke (singing to taped accompaniment)
ベクトル空間[bekutorukuukan] vector space
茜さす空[akanesasusora] glowing sky
圧搾空気[assakukuuki] compressed air
圧縮空気[asshukukuuki] compressed air

位相空間[isoukuukan] phase space (physics)
宇宙空間[uchuukuukan] outer space
雨空[amazora] rainy sky
英国航空[eikokukoukuu] British Airways
仮想空間[kasoukuukan] virtual space (e.g. in computer graphics)

ミサイル防衛[misairubouei] missile defence
共同防衛[kyoudoubouei] joint defense
攻防[koubou] offense and defense
攻防戦[koubousen] battle
国防[kokubou] national defence

国防総省[kokubousoushou] National Military Establishment
国防長官[kokubouchoukan] Secretary of Defence (Defense)
国防費[kokubouhi] defence expenditure
砂防[sabou] erosion control
酸化防止剤[sankaboushizai] antioxidant