sucrose vs brain sugar

sucrose and brain sugar both are nouns.

Word	Noun	Adjective	Verb	Adverb
sucrose	Yes	No	No	No
brain sugar	Yes	No	No	No

As nouns, brain sugar is a hyponym of sucrose; that is, brain sugar is a word with a more specific, narrower meaning than sucrose:

sucrose: a complex carbohydrate found in many plants and used as a sweetening agent
brain sugar: a simple sugar found in lactose

Other hyponyms of sucrose include galactose.

sucrose (noun)	brain sugar (noun)
a complex carbohydrate found in many plants and used as a sweetening agent	a simple sugar found in lactose