hearing aid vs acoustic device

hearing aid and acoustic device both are nouns.

Word	Noun	Adjective	Verb	Adverb
hearing aid	Yes	No	No	No
acoustic device	Yes	No	No	No

As nouns, acoustic device is a hypernym of hearing aid; that is, acoustic device is a word with a broader meaning than hearing aid:

hearing aid: a conical acoustic device formerly used to direct sound to the ear of a hearing-impaired person
acoustic device: a device for amplifying or transmitting sound

hearing aid (noun)	acoustic device (noun)
a conical acoustic device formerly used to direct sound to the ear of a hearing-impaired person	a device for amplifying or transmitting sound
an electronic device that amplifies sound and is worn to compensate for poor hearing