Sweet substance (5)
'sweet substance' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for sugar that I've seen before include "Cane or beet product" , "for such a daddy" , "Plantation product" , "Sweeten" , "Mild oath (granulated?)" .)
(Other definitions for honey that I've seen before include "Excellent; magnificent" , "sweet thing" , "Beloved" , "Made by bees from nectar" , "Love" .)
(Other definitions for treacle that I've seen before include "Saplike stuff" , "Viscous liquid" , "Sticky produce" , "Something cloyingly sweet" , "Thick, sticky, dark syrup" .)