This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
絧 combines 糸 (thread) with 同, which likely contributes the sound. The exact historical development is uncertain.
The left side is thread 糸, and the right side is 同. Without a clear meaning, picture a spool of thread that looks the same (同) from every angle.
For トウ, imagine a toe (トウ) tangled in thread (糸) that looks the same (同) as the other toes.