Move fast (6)
I believe the answer is:
hasten
'move fast' is the definition.
(hasten can mean to act or move quickly)
This is all the clue.
(Other definitions for hasten that I've seen before include "Travel with expedition" , "Hurry up in old-fashioned way" , "Athens (anag.)" , "race? - with 26a" , "Speed up" .)