acoustic modem vs modem

acoustic modem and modem both are nouns.

Word	Noun	Adjective	Verb	Adverb
acoustic modem	Yes	No	No	No
modem	Yes	No	No	No

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

acoustic modem: a modem that converts electrical signals to telephone tones and back again
modem: (from a combination of MOdulate and DEModulate) electronic equipment consisting of a device used to connect computers by a telephone line

acoustic modem (noun)	modem (noun)
a modem that converts electrical signals to telephone tones and back again	(from a combination of MOdulate and DEModulate) electronic equipment consisting of a device used to connect computers by a telephone line