The word 快乐 is formed through a meaningful fusion of two independent concepts. The first character, 快, originally meant "rapid" or "fast", but evolved in meaning to convey a sense of a "quick or light-hearted feeling" of pleasure and satisfaction. The second character, 乐, means "music" and, by deep association, the joy and delight that music brings. When combined, they create a layered idea where 快 describes the immediate, uplifting quality of the emotion, and 乐 provides the foundational essence of deep-seated joy, together forming the comprehensive sense of "happiness".