backwardness vs subnormality

backwardness and subnormality both are nouns.

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

As nouns, backwardness and subnormality are synonyms defined as:

backwardness and subnormality: lack of normal development of intellectual capacities

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

backwardness (noun)	subnormality (noun)
lack of normal development of intellectual capacities	lack of normal development of intellectual capacities
	the state of being less than normal (especially with respect to intelligence)