ataxia vs nervous disorder

ataxia and nervous disorder both are nouns.

Word	Noun	Adjective	Verb	Adverb
ataxia	Yes	No	No	No
nervous disorder	Yes	No	No	No

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

ataxia: inability to coordinate voluntary muscle movements; unsteady movements and staggering gait
nervous disorder: a disorder of the nervous system

Other hypernyms of ataxia include neurological disease, neurological disorder.

ataxia (noun)	nervous disorder (noun)
inability to coordinate voluntary muscle movements; unsteady movements and staggering gait	a disorder of the nervous system