dappled grey horse
騨 refers specifically to a dappled grey horse, a horse with a coat pattern of lighter spots on a darker background.
騨 is a phono-semantic compound combining 馬 (horse) with 単, which likely contributes the sound and may relate to the idea of a single or simple pattern, though the exact historical development is uncertain.
The left side 馬 means horse, and the right side 単 looks like a simple grid or pattern. Picture a horse with a simple dappled pattern of grey spots.
For タン, imagine a tan-colored dappled grey horse: the tan spots stand out against the grey coat, and tan -> タン.
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