Hard to resist parts with cold sweetener, perhaps (8)
I believe the answer is:
additive
'hard' is the definition.
Both the answer and definition are adjectives. Perhaps they are linked in a way I don't understand?
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for additive that I've seen before include "Such as a colorant or preservative in foodstuffs" , "Produced by summing" , "Tie David up with added substance" , "ingredient" , "Something joined, to food say" .)