The word 不光 is formed through the combination of two distinct characters, each contributing its core meaning to create a new, unified concept. The first character, 不 (bù), is a fundamental negator meaning "not". It is paired with 光 (guāng), whose primary meaning is "light" but which, in this context, leverages an extended sense of "solely" or "only" (as in being exclusively illuminated upon one thing). By fusing these elements, the compound literally conveys "not only", where the negation directly modifies the idea of exclusivity, forming an expression that inherently suggests the presence of something more beyond a single stated element.