Reform uncle had started (8)
I believe the answer is:
launched
'started' is the definition.
(launching is a kind of starting)
'reform uncle had' is the wordplay.
'reform' is an anagram indicator.
'uncle'+'had'='unclehad'
'unclehad' anagrammed gives 'LAUNCHED'.
(Other definitions for launched that I've seen before include "Propelled" , "Sent into space" , "Sent a newly-built boat into the water" , "Sent on course as uncle had" , "Set a ship in motion" .)