dead body vs remains

dead body and remains both are nouns.

Word	Noun	Adjective	Verb	Adverb
dead body	Yes	No	No	No
remains	Yes	No	No	No

As nouns, remains is a hyponym of dead body; that is, remains is a word with a more specific, narrower meaning than dead body:

Other hyponyms of dead body include kill, carcase, carcass, carrion, roadkill, cadaver, clay, corpse, stiff, mummy.

dead body (noun)	remains (noun)
a natural object consisting of a dead animal or person	the dead body of a human being
	any object that is left unused or still extant
	a relic that has been excavated from the soil