slowness vs subnormality

slowness and subnormality both are nouns.

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

As nouns, slowness and subnormality are synonyms defined as:

slowness and subnormality: lack of normal development of intellectual capacities

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

slowness (noun)	subnormality (noun)
a rate demonstrating an absence of haste or hurry	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)
unskillfulness resulting from a lack of training