The word 不许 is formed through the direct and logical combination of two independent characters: 不 (bù), which means "not" or "no", and 许 (xǔ), which means "to allow" or "to permit". These two concepts are merged into a single unit where the meaning of the first character negates the action of the second, creating a new, unified concept of prohibition or denial of permission. It is a straightforward semantic fusion where the whole meaning is essentially the sum of its prohibitive parts.