delirium vs mental disorder

delirium and mental disorder both are nouns.

Word	Noun	Adjective	Verb	Adverb
delirium	Yes	No	No	No
mental disorder	Yes	No	No	No

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

delirium: a usually brief state of excitement and mental confusion often accompanied by hallucinations
mental disorder: (psychiatry) a psychological disorder of thought or emotion; a more neutral term than mental illness

Other hypernyms of delirium include disturbance, folie, mental disturbance, psychological disorder.

delirium (noun)	mental disorder (noun)
a usually brief state of excitement and mental confusion often accompanied by hallucinations	(psychiatry) a psychological disorder of thought or emotion; a more neutral term than mental illness
state of violent mental agitation