cotton, silk
纊 centers on fine natural fibers used for textiles: cotton and silk. Both meanings point to soft, thread-like materials that can be spun or woven.
纊 combines 糸 (thread) with 廣, which likely contributes the sound. The character is used for cotton and silk, but the exact historical development of the right component is uncertain.
The left side 糸 is thread. The right side 廣 looks like a wide, spreading shape. Imagine a wide field of cotton plants or silkworms producing endless fine thread.
For コウ, picture a cocoon of silk: cocoon -> コウ, and the thread 糸 comes from the cocoon.