Where the shape comes from
A bone joint, its socket or marrow cavity shown at the top, set above 肉, flesh, the meat radical worn down to 月 — bone shown together with what covers it. It names the bone itself in 骨头 and 骨折, a fracture, and extends, the way English speaks of backbone, to 骨气, moral integrity, the inner structure of a person’s character.
汉字 filed under 骨
No published character on HSK Guide is filed under this radical yet. 汉字库.