'Sucre', oft translated as 'sugar' (8)
I believe the answer is:
'sugar' is the definition.
(I know that fructose is a type of ketohexose)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for fructose that I've seen before include "Sweetener" , "It's sweet" , "Kind of sugar" , "A simple sugar, in honey for instance" , "Fruit-sugar" .)