Be ambitious (6)
I believe the answer is:
aspire
'be ambitious' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for aspire that I've seen before include "I spare (anag.)" , "Aim, have an ambitious plan" , "Is a rep (anag.)" , "Hope (to do something)" , "Desire (to reach higher things)" .)