slight vs slightness

slight and slightness both are nouns.

Word	Noun	Adjective	Verb	Adverb
slight	Yes	Yes	Yes	No
slightness	Yes	No	No	No

slight (noun)	slightness (noun)
a deliberate discourteous act (usually as an expression of anger or disapproval)	slenderness
	the property of an attractively thin person
	the quality of being unimportant and petty or frivolous

slight (adjective)	slightness (adjective)
(quantifier used with mass nouns) small in quantity or degree; not much or almost none or (with `a') at least some
lacking substance or significance
being of delicate or slender build

slight (verb)	slightness (verb)
pay no attention to, disrespect