Aim high (6)
I believe the answer is:
aspire
'aim high' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for aspire that I've seen before include "Have a strong desire to reach an objective" , "Have lofty aims" , "Desire (to reach higher things)" , "Yearn, dream (towards)" , "Earnestly desire (to achieve something)" .)