gallop, rush about, pursue, run
騖 centers on rapid, driven movement: galloping, rushing about, or pursuing something at speed. The idea of running is the common thread.
騖 combines 馬 (horse) with 敄, which likely contributes the sound and suggests forceful action. The character originally referred to a horse galloping or rushing.
A horse (馬) under the top component 敄, which looks like a person urging it on. Picture a rider spurring a horse to gallop and rush forward.
For ブ, imagine a horse galloping so fast it makes a booming sound: boo -> ブ. The horse rushes with a loud boo.