Study article penned by socialist (4)
I believe the answer is:
read
'study' is the definition.
(I know that study can be written as read)
'article penned by socialist' is the wordplay.
'article' becomes 'a' (English indefinite article).
'penned by' means one lot of letters goes inside another (inserted letters are penned in).
'socialist' becomes 'red' (red can informally mean a socialist).
'a' put within 'red' is 'READ'.
(Other definitions for read that I've seen before include "Check, emend (proof)" , "Use a book" , "Interpret writing" , "Study (for a degree?)" , "See - peruse - understand" .)