Desire for success (8)
I believe the answer is:
ambition
'desire for success' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for ambition that I've seen before include "Desire (for riches, fame)" , "I'm in boat (anag.)" , "Strong drive for success" , "Strong desire for success" , "Urge to better oneself" .)