Origin

The character 肩 combines two components to represent the shoulder. The left part 戸 acts as a frame or enclosure, while 月 on the right represents flesh or body—in this case, the meaty part of the shoulder. Together, they picture the shoulder as a distinct, fleshy part of the body, enclosed or defined as a separate section. Over time, this visual combination became the standard way to write the word for shoulder in Japanese.