an excellent horse
驊 centers on a horse of exceptional quality: an excellent, fine horse.
驊 combines 馬 (horse) with 華, which likely contributes the sound and may suggest splendor or excellence, fitting the meaning of an excellent horse.
A horse 馬 that is as splendid as a flower 華: 驊 is an excellent horse.
For カ, imagine a car that is as excellent as this horse: car -> カ, and the horse is so fine it could outrun any car.
fine horse; swift horse