Socialist in upturn shows apathy (7)
I believe the answer is:
boredom
'apathy' is the definition.
(thesaurus)
'socialist in upturn' is the wordplay.
'socialist' becomes 'red' (socialism is often associated with the colour red).
'in' is an insertion indicator.
'upturn' becomes 'boom' (I am not sure about this - if you are sure you should believe this answer much more).
'red' put into 'boom' is 'BOREDOM'.
'shows' is the link.
Can you help me to learn more?
(Other definitions for boredom that I've seen before include "no interest" , "Mental state" , "Overseers" , "Monotony" , "Feeling" .)