idiocy vs subnormality

idiocy and subnormality both are nouns.

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

As nouns, subnormality is a hypernym of idiocy; that is, subnormality is a word with a broader meaning than idiocy:

Other hypernyms of idiocy include backwardness, mental retardation, retardation, slowness.

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