Hone
The Japanese word "hone" (骨) means "bone" in English. It is used to refer to the core elements of a tree, such as root parts, trunks and thick branches, which cannot be remade easily. "Hone" can decide the individuality of a tree and is an important factor in bonsai art.
The English word "hone" means to sharpen or refine something, especially a skill or an instrument, such as a bonsai cutting tool.