epilepsy vs brain disorder

epilepsy and brain disorder both are nouns.

Word	Noun	Adjective	Verb	Adverb
epilepsy	Yes	No	No	No
brain disorder	Yes	No	No	No

As nouns, brain disorder is a hypernym of epilepsy; that is, brain disorder is a word with a broader meaning than epilepsy:

epilepsy: a disorder of the central nervous system characterized by loss of consciousness and convulsions
brain disorder: any disorder or disease of the brain

Other hypernyms of epilepsy include brain disease, encephalopathy.

epilepsy (noun)	brain disorder (noun)
a disorder of the central nervous system characterized by loss of consciousness and convulsions	any disorder or disease of the brain