ineptness vs slowness

ineptness and slowness both are nouns.

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

As nouns, ineptness and slowness are synonyms defined as:

ineptness and slowness: unskillfulness resulting from a lack of training

Other synonyms of ineptness include awkwardness, clumsiness, ineptitude, maladroitness.

ineptness (noun)	slowness (noun)
the quality of having the wrong properties for a specific purpose	a rate demonstrating an absence of haste or hurry
unskillfulness resulting from a lack of training	lack of normal development of intellectual capacities
	unskillfulness resulting from a lack of training