slightness vs slight

slightness and slight both are nouns.

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

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

slightness (adjective)	slight (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

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