a small tower on top of a wall or building, especially a castle （尤指城堡的）塔楼，角楼 
a small metal tower on a ship, plane or tank that can usually turn around and from which guns are fired （战舰、飞机或坦克的）炮塔，回转炮塔，活动射击装置 a gun turret 炮塔
Word OriginMiddle English: from Old French tourete, diminutive of tour ‘tower’.