The word "褪黑素" is formed by combining the character "褪", meaning to fade or shed, with "黑", meaning black or darkness, and ending with "素", meaning substance or element; the compound "褪黑" conceptually describes the fading of darkness, and when combined with "素" it specifies a biochemical substance, directly referring to melatonin, which is involved in regulating sleep cycles in response to darkness.