turns, twists, switch
紾 centers on twisting or turning something, especially in the context of threads or cords. The meanings of turns, twists, and switch all relate to changing direction or orientation.
紾 combines 糸 (thread) with 㐱, which likely contributes a phonetic element. The character is associated with twisting or turning threads, but the exact historical development of the right component is uncertain.
The left side 糸 is thread, and the right side 㐱 looks like a twisted shape. Imagine twisting threads together until they form a tight switch.
For シン, picture a thin thread being twisted: thin -> シン, and the thread turns and twists.