Have ambition (6)
I believe the answer is:
aspire
'have ambition' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for aspire that I've seen before include "Yearn, dream (towards)" , "Have ambitions (to achieve something)" , "Have an ambitious plan or a lofty goal" , "Have a strong desire to achieve something" , "Set your sights on" .)