retarded vs precocious

retarded is a noun but precocious is not a noun.

Word	Noun	Adjective	Verb	Adverb
retarded	Yes	Yes	No	No
precocious	No	Yes	No	No

retarded (noun)	precocious (noun)
people collectively who are mentally retarded

retarded (adjective)	precocious (adjective)
relatively slow in mental or emotional or physical development	characterized by or characteristic of exceptionally early development or maturity (especially in mental aptitude)
	appearing or developing early