When someone says "light as a feather," they are referring to something that is extremely light and weightless. There are numerous synonyms for this phrase, such as "airy," "ethereal," "fluffy," "feathery," "gossamer," "delicate," "floaty," "weightless," "diaphanous," "sheer," "fleecy," and "soft." These words can be used to describe a variety of things, including fabrics, clouds, hair, pillows, and even moods. By using these synonyms, a writer can add more depth and variety to their language, making their writing more creative and engaging to a reader.