The word 嘴唇 is formed by combining two characters, each representing a distinct but related part of the whole concept. The first character, 嘴, specifically means "mouth", referring to the entire opening. The second character, 唇, means "lip", the fleshy, defining border of that opening. By placing them together, the concept is visually and functionally built from the general area (嘴) to its most prominent and defining feature (唇), merging into the single, precise idea of "lips" as the physical edge of the mouth.