idiocy vs slowness

idiocy and slowness both are nouns.

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

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

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

idiocy (noun)	slowness (noun)
extreme mental retardation	a rate demonstrating an absence of haste or hurry
	lack of normal development of intellectual capacities
	unskillfulness resulting from a lack of training