The silk radical (left-side form of 糸) marks 纱 as a kind of woven fabric. It joins 线, 织, 绸 in the textile family, where threads cross to make cloth - here a thin, sheer cloth such as gauze or muslin.
Provides the sound, drifting from shǎo to shā. The few meaning even works as a memory hook: gauze is woven with few threads, so the cloth is sparse and see-through - a thin fabric defined by what is missing.
