He's out of work but remains optimistic (5)
I believe the answer is:
hopes
'remains optimistic' is the definition.
I can't judge whether this defines the answer.
'he's out of work but' is the wordplay.
'out of' is an insertion indicator (some letters on the outside of others).
'work but' becomes 'op' (abbreviation for opus. I am not sure about the 'but' bit.).
'hes' placed around 'op' is 'HOPES'.
Can you help me to learn more?
(Other definitions for hopes that I've seen before include "Aspirations, wishes" , "Believes that good things may happen" , "Desires and expects" , "Aspires" , "Expectations" .)