Optimist's feeling (4)
I believe the answer is:
hope
'optimist's feeling' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for hope that I've seen before include "writer" , "It goes with faith and charity" , "Aspiration" , "Bob --, US comic" , "English-born US comedian, d. 2003" .)