Without leader, nearer failure (5)
I believe the answer is:
loser
'failure' is the definition.
(synonyms)
'without leader nearer' is the wordplay.
'without leader' means to remove the first letter.
'nearer' becomes 'closer' (synonyms).
'closer' with its initial letter taken off is 'LOSER'.
(Other definitions for loser that I've seen before include "one that's been left behind" , "Unsuccessful contestant" , "One not winning" , "Washout" , "Opposite of winner" .)