pongee (a knotted silk cloth)
紬 centers on a specific type of silk fabric: pongee, which is made from knotted or hand-spun silk threads. The meaning is narrow and concrete, referring to the cloth itself.
紬 combines 糸 (thread/silk) with 由, which likely contributes the sound. The character was created to name a specific type of silk fabric.
The left side 糸 is thread, and the right side 由 looks like a spool or a knot. Picture silk threads being knotted together on a spool to make pongee cloth.
For チュウ, imagine chewing on a piece of pongee silk (don't actually do it!): chew -> チュウ, and the fabric is so soft it feels like you could chew it.
tsumugi; pongee; traditional rough-surfaced cloth woven from raw silk
Oshima tsumugi weave (type of pongee made in the Amami islands)
white pongee
tsumugi silk yarn; (spun) silk noil yarn
yellowfin toxic goby (Yongeichthys criniger); horny goby
silk products produced near Yūki (using natural indigo dye); Yūki pongee
pongee (unbleached silk)