backward vs retarded

backward is not a noun while retarded is a noun.

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

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

backward (adjective)	retarded (adjective)
directed or facing toward the back or rear	relatively slow in mental or emotional or physical development
(used of temperament or behavior) marked by a retiring nature
retarded in intellectual development
having made less than normal progress

backward (adverb)	retarded (adverb)
in a manner or order or direction the reverse of normal
in or to or toward a past time
at or to or toward the back or rear