backwardness vs retardation

backwardness and retardation both are nouns.

Word	Noun	Adjective	Verb	Adverb
backwardness	Yes	No	No	No
retardation	Yes	No	No	No

As nouns, backwardness and retardation are synonyms defined as:

backwardness and retardation: lack of normal development of intellectual capacities

Other synonyms of backwardness include mental retardation, slowness, subnormality.

backwardness (noun)	retardation (noun)
lack of normal development of intellectual capacities	the act of slowing down or falling behind
	a decrease in rate of change
	lack of normal development of intellectual capacities
	any agent that retards or delays or hinders
	the extent to which something is delayed or held back