Pretty trim sweetheart (4)
I believe the answer is:
cute
'pretty' is the definition.
(thesaurus)
'trim sweetheart' is the wordplay.
'trim' becomes 'cut' ('cut' can be a synonym of 'trim'**).
'sweetheart' becomes 'e' (the heart/centre of 'sweet').
'cut'+'e'='CUTE'
(Other definitions for cute that I've seen before include "Quaintly pleasing" , "Location" , "Lovable" , "Clever - attractive" , "Sweet, attractive" .)