Late decree — ordered to slow down (10)
I believe the answer is:
decelerate
'slow down' is the definition.
(synonyms)
'late decree ordered' is the wordplay.
'ordered' indicates anagramming the letters.
'late'+'decree'='latedecree'
'latedecree' anagrammed gives 'DECELERATE'.
'to' is the link.
(Other definitions for decelerate that I've seen before include "Slow down" , "Move more slowly" , "Reduce speed" , "ease up" .)