horn, flageolet
篥 refers to a type of wind instrument: a horn or a flageolet, both of which are musical instruments that produce sound by blowing.
篥 combines 竹 (bamboo) with 栗 (chestnut), likely as a phono-semantic compound where 栗 contributes the sound and bamboo indicates a bamboo-made instrument.
Bamboo 竹 on top suggests a bamboo instrument, and the bottom 栗 looks like a chestnut-shaped wind instrument. Imagine a horn made from bamboo with a chestnut-like bulb at the end.
For リキ, picture a leaky horn: when you blow into this bamboo instrument, air leaks out with a 'riki' sound. Leaky -> リキ.
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small double-reed wind instrument used in gagaku (made of bamboo, with 7 holes on top and 2 below)