The word '洗发皂' is formed by sequentially combining the characters 洗 (wash), 发 (hair), and 皂 (soap), where each character contributes a specific semantic component: 洗 denotes the action of cleaning, 发 specifies the object of that action, and 皂 identifies the material used, resulting in a compound term that literally means "wash-hair-soap" or a soap product for cleaning hair.