Sicken with sweetness (4)
I believe the answer is:
cloy
'sicken with sweetness' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for cloy that I've seen before include "Make weary through over-sentimentality" , "Sicken by glutting" , "Get rather rich" , "Be sickeningly sweet" , "Sicken with sentiment" .)