lock
鑰 centers on a physical lock, specifically the metal key or locking mechanism itself.
鑰 combines 金 (metal) with 龠, which likely contributes the sound and may relate to a flute-like tube, suggesting a metal locking device.
The metal radical 金 on the left hints at a metal object, and the right side 龠 looks like a complex mechanism. Picture a heavy metal lock with an intricate keyhole.
For ヤク, imagine a yak carrying a large metal lock on its horn: yak -> ヤク, and the lock keeps the yak's treasure safe.