sound alphabet vs alphabet

sound alphabet and alphabet both are nouns.

Word	Noun	Adjective	Verb	Adverb
sound alphabet	Yes	No	No	No
alphabet	Yes	No	No	No

As nouns, alphabet is a hypernym of sound alphabet; that is, alphabet is a word with a broader meaning than sound alphabet:

sound alphabet: an alphabet of characters intended to represent specific sounds of speech
alphabet: a character set that includes letters and is used to write a language

Other hypernyms of sound alphabet include ABC's, ABC, ABCs.

sound alphabet (noun)	alphabet (noun)
an alphabet of characters intended to represent specific sounds of speech	the elementary stages of any subject (usually plural)
	a character set that includes letters and is used to write a language