An aqualung is the equipment a diver wears on their back so they can breathe under water: tanks of air plus the parts that feed that air to the mouth. The name was first a brand — Aqua-Lung — for the open-circuit scuba set that Émile Gagnan and Jacques Cousteau made in 1943. From there it became, for many English speakers, a general word for that kind of breathing gear. Younger divers and textbooks now often say scuba or scuba gear instead; aqualung can sound a little older, the word you meet in adventure books and museum cards. People also stretch it to mean the whole “tank on the back” picture, even when they are not being careful about which piece is which. It is built from aqua- (“water”) and lung — as if you were taking extra lungs with you into the water.

水肺、水中呼吸器（背在背上、讓人在水裡呼吸的裝備）。台灣潛水界更常說 scuba 或「水肺潛水」；aqualung 原是商品名，後來也當通稱。