decibel vs sound unit

decibel and sound unit both are nouns.

Word	Noun	Adjective	Verb	Adverb
decibel	Yes	No	No	No
sound unit	Yes	No	No	No

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

decibel: a logarithmic unit of sound intensity; 10 times the logarithm of the ratio of the sound intensity to some reference intensity
sound unit: any acoustic unit of measurement

decibel (noun)	sound unit (noun)
a logarithmic unit of sound intensity; 10 times the logarithm of the ratio of the sound intensity to some reference intensity	any acoustic unit of measurement