cord
紃 centers on a cord or braided strand, typically made from thread or silk.
紃 combines 糸 (thread) with 川, which likely contributes the sound and may suggest the flowing, braided shape of a cord.
Thread 糸 flowing like a river 川 forms a braided cord.
For シュン, imagine a cord snapping with a sharp 'shun' sound: shun -> シュン, as the thread strands twist together.