caries vs tooth decay

caries and tooth decay both are nouns.

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

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

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

Other synonyms of caries include cavity, dental caries.

caries (noun)	tooth decay (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