Follow an order (4)
I believe the answer is:
obey
'follow an order' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for obey that I've seen before include "Do as one's told" , "Act in accordance with (law)" , "Perversely inclined to do the opposite" , "Carry out (orders)" , "Hear" .)