The term "lighter-than-water" refers to materials or substances that have a lower density than water, causing them to float on its surface. Some synonyms for "lighter-than-water" include "buoyant," "floaty," "airy," and "effervescent." "Buoyant" indicates something that is able to float easily on the surface of water because of its light weight. "Floaty" is a casual synonym for buoyant, often used in a playful or whimsical manner. "Airy" refers to something that is light and delicate, sometimes used to describe a feeling or mood of lightheartedness. "Effervescent" refers to something that bubbles or fizzes, often used to describe drinks or carbonated substances that are lighter-than-water.