Sweetheart meets up for appreciation (6)
I believe the answer is:
esteem
'appreciation' is the definition.
(thesaurus)
'sweetheart meets up' is the wordplay.
'sweetheart' becomes 'e' (the heart/centre of 'sweet').
'up' shows that the letters should be reversed in order (in down clue: letters go upwards).
'meets' back-to-front is 'steem'.
'e'+'steem'='ESTEEM'
'for' is the link.
(Other definitions for esteem that I've seen before include "Favourable regard" , "High regard as for customer" , "Consider" , "Respect, admire" , "Revere - prize" .)