acousma vs hallucination

acousma and hallucination both are nouns.

Word	Noun	Adjective	Verb	Adverb
acousma	Yes	No	No	No
hallucination	Yes	No	No	No

As nouns, hallucination is a hypernym of acousma; that is, hallucination is a word with a broader meaning than acousma:

acousma: illusory auditory perception of strange nonverbal sounds
hallucination: illusory perception; a common symptom of severe mental disorder

acousma (noun)	hallucination (noun)
illusory auditory perception of strange nonverbal sounds	a mistaken or unfounded opinion or idea
	an object perceived during a hallucinatory episode
	illusory perception; a common symptom of severe mental disorder