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

掩蓋[engai] cover(ing)
掩護部隊[engobutai] covering force
掩蔽[enpei] cover
掩い[ooi] cover
掩護[engo] covering

掩う[oou] to cover
掩壕[engou] cover trench
顔を掩う[kaowooou] to cover one's face
掩護射撃[engoshageki] (providing) covering fire
掩撃[engeki] sneak attack (by a small group)