delirium vs mental disturbance

delirium and mental disturbance both are nouns.

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

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

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

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

delirium (noun)	mental disturbance (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