A leader at the front (5)
I believe the answer is:
ahead
'at the front' is the definition.
(synonyms)
'a leader' is the wordplay.
'leader' becomes 'head' (head is a kind of leader).
'a'+'head'='AHEAD'
(Other definitions for ahead that I've seen before include "In the leading position" , "at pole" , "likely to win?" , "Winning" , "What's down the road" .)