Bit of a quiet socialist (5)
I believe the answer is:
shred
'bit' is the definition.
(I know that bit can be written as shred)
'a quiet socialist' is the wordplay.
'a quiet' becomes 'sh' ('sh' is used to tell someone to be quiet).
'socialist' becomes 'red' (socialism is often associated with the colour red).
'sh'+'red'='SHRED'
'of' is the link.
(Other definitions for shred that I've seen before include "(Tear into) small piece(s)" , "Tiny amount" , "Cut into tiny pieces" , "Cut finely" , "Bit of rag" .)