Blush in socialist lair (6)
I believe the answer is:
redden
'blush' is the definition.
(I know that blush can be written as redden)
'socialist lair' is the wordplay.
'socialist' becomes 'red' (socialism is often associated with the colour red).
'lair' becomes 'den' (synonyms).
'red'+'den'='REDDEN'
'in' is the link.
(Other definitions for redden that I've seen before include "Give visible sign of embarrassment" , "Blush, colour accordingly" , "Blush or become flushed" , "Evaluate the nature of (something)" , "Reveal embarrassment in colourful way" .)