tooth decay vs cavity

tooth decay and cavity both are nouns.

Word	Noun	Adjective	Verb	Adverb
tooth decay	Yes	No	No	No
cavity	Yes	No	No	No

As nouns, tooth decay and cavity are synonyms defined as:

tooth decay and cavity: soft decayed area in a tooth; progressive decay can lead to the death of a tooth

Other synonyms of tooth decay include caries, dental caries.

tooth decay (noun)	cavity (noun)
soft decayed area in a tooth; progressive decay can lead to the death of a tooth	(anatomy) a natural hollow or sinus within the body
	a sizeable hole (usually in the ground)
	soft decayed area in a tooth; progressive decay can lead to the death of a tooth
	space that is surrounded by something