The word 发誓 is formed by combining two characters: 发, which carries the core idea of "issuing forth" or "emitting", and 誓, which means "oath" or "pledge" and is itself a vivid conceptual composite of 言 (speech) over 折 (to break or bend), historically implying a solemn verbal declaration where breaking it would cause a rupture. Together, they create a single conceptual unit that visually and notionally represents the act of "issuing forth a solemn pledge", capturing the moment a vow is actively put into words and released into the world.