The word 亲口 is formed by combining two characters whose core meanings create a vivid, metaphorical image. The first character, 亲, carries the idea of personal closeness, directness, and doing something oneself. The second, 口, literally means "mouth", representing the act of speaking. When fused, they do not simply add together but conceptually layer to mean "personally by one's own mouth", picturing the speaker physically and intimately close to the utterance to emphasize firsthand, direct testimony or a promise made without intermediation.