tie-dyeing, purblind
纈 centers on tie-dyeing, a resist-dyeing technique where fabric is bound to create patterns. The rare meaning 'purblind' likely refers to a blurred or indistinct vision, metaphorically extending the idea of bound or obscured clarity.
纈 combines 糸 (thread) with 頡, which likely contributes the sound. The character is associated with bound thread in tie-dyeing, but the exact historical development is uncertain.
The left side 糸 is thread, and the right side 頡 looks like a complex knot. Picture threads tightly bound around fabric to resist dye, creating the patterns of tie-dyeing.
For ケツ, imagine tying knots in fabric while wearing a kets (a made-up word for a special dyeing apron): kets -> ケツ, and the knots create the tie-dye pattern.
style of tie-dyeing used during the Nara era