Other forms: aqualungs
If your life's ambition is to live underwater like a mermaid, you'd better get practicing on how to use an aqualung, an underwater breathing system.
An aqualung is a kind of diving equipment that lets you breathe under water. It's an air tank strapped to your back plus a mouthpiece that lets you breathe in that air. Its name was the brand name of the first ever underwater breathing apparatus, what we now call scuba equipment. There have been lots of developments in scuba diving since then, but many of them are based on the aqualung.