black horse
驔 is a rare kanji that refers specifically to a black horse. Its meaning is narrow and concrete, with no broader conceptual center beyond that single image.
驔 combines 馬 (horse) with 覃, which likely contributes the sound. The exact historical development of 覃 within this character is uncertain, but the structure is a typical phono-semantic compound for a specific type of horse.
The left side is a horse 馬, and the right side 覃 looks like a dark, deep container. Picture a horse emerging from deep shadow, its coat so dark it seems to absorb light: a black horse.
For テン, imagine ten black horses galloping together: ten -> テン, and all ten are the same deep black.