medicine, chemical, enamel, gunpowder, benefit
藥 centers on substances used to treat or alter: medicine for healing, chemicals for practical use, enamel as a coating, gunpowder as an explosive mixture, and benefit as the positive effect they bring.
藥 combines 艹 (grass/plant) with 樂, which likely contributes the sound and originally referred to music or enjoyment. The plant connection points to herbal medicine, while the phonetic element suggests a soothing or beneficial effect.
The top grass radical 艹 hints at plants, and the lower 樂 looks like a complex mixture. Picture herbs and ingredients being ground together into a potent medicine or chemical paste.
For ヤク, imagine a yak chewing medicinal herbs: yak -> ヤク, and the yak's herbal snack becomes a healing remedy.