This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
綋 combines 糸 (thread) with 宏, which likely contributes sound. The exact historical development is uncertain.
The left side is thread 糸, and the right side is 宏, which suggests something broad or large. Picture a thick, broad rope made of many threads.
For コウ, imagine a broad rope coiling around a post: coil -> コウ, and the thread 糸 forms the rope.