reel, hank, skein, (kokuji)
桛 centers on a tool for winding thread or yarn: a reel, hank, or skein. It is a Japanese kokuji, so its meaning is tied to this specific object rather than a broad abstract concept.
桛 is a Japanese kokuji created by combining 木 (wood) with a right side that visually suggests 上 (up) over 下 (down), possibly representing a wooden frame for winding thread. The exact historical origin is uncertain.
The left side 木 (tree/wood) suggests a wooden tool, and the right side looks like 上 (up) over 下 (down), like thread being wound up and down around a reel. Picture a wooden spool spinning thread into a neat hank.
For カセ, imagine a wooden reel covered in a thick case of thread: case -> カセ, and the case holds the skein tightly.