tooth decay vs caries

tooth decay and caries both are nouns.

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

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

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

Other synonyms of tooth decay include cavity, dental caries.

tooth decay (noun)	caries (noun)
soft decayed area in a tooth; progressive decay can lead to the death of a tooth	soft decayed area in a tooth; progressive decay can lead to the death of a tooth