The word "妖怪" is formed by combining the characters "妖" and "怪". "妖" consists of the radical "女" (woman) and the phonetic component "夭" (yāo), denoting a demon or supernatural being often associated with eeriness. "怪" consists of the radical "忄" (heart/mind) and the phonetic component "圣" (guài), denoting strangeness or something monstrous. Together, they create a compound where both characters contribute semantically to the meaning of a monster or supernatural creature, emphasizing an unnatural and unsettling entity.