Some optimism returns after reflecting for a period (4)
I believe the answer is:
term
'period' is the definition.
(I know that period can be written as term)
'some optimism returns after reflecting' is the wordplay.
'some' indicates a hidden word (some of the parts of the word are used).
'after reflecting' is a reversal indicator.
'mret' can be found hidden inside 'optimism returns'.
'mret' reversed gives 'TERM'.
'for a' acts as a link.
(Other definitions for term that I've seen before include "Period of education" , "Limited period; school session" , "Word or expression and period of time" , "Part of the school year" , "Limited period of time" .)