name of a famous horse
驌 is a rare kanji that refers specifically to the name of a famous horse. Its meaning is limited to this proper-name usage.
驌 combines 馬 (horse) with 肅, which likely contributes the sound. The character was created as a proper name for a specific horse, so its structure is phono-semantic.
A horse 馬 paired with the sound component 肅: this is the name of a famous horse. Picture a legendary steed with a name that sounds like シュク.
For シュク, imagine the famous horse named Shuku, a sleek black stallion: Shuku -> シュク.
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