flute
龠 centers on a flute, specifically an ancient Chinese wind instrument with multiple pipes. The meaning is narrow and concrete, referring to the instrument itself.
龠 is a pictograph of a panpipe-like wind instrument, with the top representing the mouthpiece and the lower part the bundled pipes. The modern form retains this general shape.
The top looks like a mouthpiece, and the lower part resembles a set of vertical pipes bound together. Picture an ancient flute made of multiple tubes: 龠 is that flute.
For ヤク, imagine a yak playing a flute: yak -> ヤク, and the yak's breath produces music through the pipes.