Native American releasing horse quickly (5)
I believe the answer is:
apace
'quickly' is the definition.
(I know that quickly can be written as apace)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for apace that I've seen before include "at high speed" , "fast" , "What's quickly" , "flat out" , "Quick" .)