sacrifice
禴 centers on a ritual offering or sacrifice, particularly a spring or summer purification rite. Its meaning is narrow and ceremonial.
禴 combines 示 (altar, spirit) with 龠 (a reed instrument used in rituals), suggesting a musical sacrifice or offering. The exact historical development is uncertain.
The left side 示 is an altar, and the right side 龠 looks like a complex ritual instrument. Picture a priest at the altar playing a reed pipe to offer a sacrifice.
For ヤク, imagine a yak being led to the altar as a sacrifice: yak -> ヤク, and the ritual music plays.