Sweet betrothal partly rejected (5)
I believe the answer is:
torte
'sweet' is the definition.
(I know that torte is a type of sweet)
'betrothal partly rejected' is the wordplay.
'partly' indicates a hidden word (part of the clue is used).
'rejected' says the letters should be written backwards.
'etrot' is hidden within 'betrothal'.
'etrot' back-to-front is 'TORTE'.
(Other definitions for torte that I've seen before include "Sweet cake or tart" , "Rich food" , "Rich (Austrian) cake or pastry" , "German cream cake" , "1d [PASTRY]" .)