Most sugary or mellifluous (8)
I believe the answer is:
sweetest
'most sugary or mellifluous' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for sweetest that I've seen before include "Most Melliflous" , "dearest" , "Most saccharine or sugary" , "most attractive" , "Most winsome" .)