Charming sweetheart follows fashion (4)
I believe the answer is:
cute
'charming' is the definition.
(I've seen this in other clues)
'sweetheart follows fashion' is the wordplay.
'sweetheart' becomes 'e' (the heart/centre of 'sweet').
'follows' says to put letters next to each other.
'fashion' becomes 'cut' (cut is a kind of fashion**).
'e' put after 'cut' is 'CUTE'.
(Other definitions for cute that I've seen before include "Endearing" , "Attractive or quaint, as in America" , "Winsome" , "Pretty and attractive" , "Sweet, attractive" .)