cord
纆 centers on a cord or rope, specifically a type of cord used for binding or measuring. The single given meaning 'cord' is the core idea.
纆 combines 糸 (thread) with 墨, which likely contributes the sound and possibly the idea of a dark or marked cord. The exact historical development is uncertain.
The left side 糸 is thread, and the right side 墨 means ink. Imagine a cord dipped in ink, used for marking straight lines in carpentry—a cord.
For ボク, picture a box of cords: box -> ボク, and the cord is coiled inside.