cross-stitch, darn
縢 centers on mending fabric with thread: cross-stitching and darning, both ways of repairing or reinforcing cloth by sewing.
縢 combines 糸 (thread) with 朕 (a phonetic component suggesting the sound トウ), forming a character about sewing or stitching. The exact historical development of the right side is uncertain, but the phono-semantic structure is clear.
The thread radical 糸 is wrapped around the right side like stitches holding fabric together. Picture cross-stitching a darn over a tear.
For トウ, imagine darning a toe of a sock: toe -> トウ, and you stitch the hole closed with thread.