Not entirely stupid -- a hopeful state (5)
I believe the answer is:
idaho
'state' is the definition.
(Idaho is an example)
'not entirely stupid a hopeful' is the wordplay.
'not entirely' says the answer is hidden in the clue.
'IDAHO' is hidden within 'stupid a hopeful'.
(Other definitions for idaho that I've seen before include "Another state" , "US state E. of Oregon" , "State of NW US" , "State of north-west USA" , "US location" .)