Optimistic; flushed (4)
I believe the answer is:
rosy
This clue is a double definition.
'optimistic' is the first definition.
(similar in meaning)
'flushed' is the second definition.
(I know that flushed can be written as rosy)
(Other definitions for rosy that I've seen before include "Of the future, promising like flower" , "Healthy-looking" , "Promising; hopeful" , "Pink; promising" , "lady" .)