The word "大小" is formed through the direct, complementary pairing of two opposite and fundamental characters: "大" (big) and "小" (small). This juxtaposition does not merely list the two extremes but fuses them into a single, abstract concept representing the collective property of "size" or "dimension". It is a conceptual compound where the whole, the idea of magnitude or scale, emerges from the relationship between its contrasting parts.