Today was successful, looking back (3)
I believe the answer is:
now
'today' is the definition.
(synonyms)
'was successful looking back' is the wordplay.
'was successful' becomes 'won' (I've seen this in another clue).
'looking back' shows that the letters should be reversed in order.
'won' backwards is 'NOW'.
(Other definitions for now that I've seen before include "Today" , "Immediately" , "At present, this instant" , "The present moment" , "At this moment in time" .)