slowness vs imbecility

slowness and imbecility both are nouns.

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

As nouns, imbecility is a hyponym of slowness; that is, imbecility is a word with a more specific, narrower meaning than slowness:

slowness: lack of normal development of intellectual capacities
imbecility: retardation more severe than a moron but not as severe as an idiot

slowness (noun)	imbecility (noun)
a rate demonstrating an absence of haste or hurry	a stupid mistake
lack of normal development of intellectual capacities	retardation more severe than a moron but not as severe as an idiot
unskillfulness resulting from a lack of training