Touch up sweetheart girlfriend (4)
I believe the answer is:
date
'girlfriend' is the definition.
(I've seen this in other clues)
'touch up sweetheart' is the wordplay.
'touch' becomes 'tad' (I've seen this in other clues**).
'up' shows that the letters should be reversed in order (in down clue: letters go upwards).
'sweetheart' becomes 'e' (the heart/centre of 'sweet').
'tad' back-to-front is 'dat'.
'dat'+'e'='DATE'
(Other definitions for date that I've seen before include "The fruit for a social engagement" , "Stoned fruit" , "Estimate age of" , "See 12" , "Sweet fruit with a long woody seed" .)