famous horse
騮 centers on a specific type of horse: a famous or renowned horse, often with a dark mane or tail. The meaning is narrow and refers to a celebrated steed.
騮 combines 馬 (horse) with 留, which likely provides the sound and may relate to the idea of a horse that stays or is kept, but the exact historical development is uncertain.
A horse (馬) that is kept (留) and celebrated becomes a famous horse. Picture a legendary steed with a dark mane, tied to a post, admired by all.
For リュウ, imagine a famous horse named Ryu, like a dragon (竜, リュウ) among horses: Ryu -> リュウ, and this steed is as legendary as a dragon.
fine horse; swift horse