The word 顶级 is formed by combining two characters: 顶, meaning "peak" or "top", and 级, meaning "level" or "grade". It is a direct conceptual fusion where the idea of the highest point (顶) is applied to a scale or ranking system (级), creating a new term that signifies the "top level" or "highest grade". This formation relies on a logical, metaphorical relationship where one element modifies the other to express a superlative category.