abrupt vs abruptness

abrupt is not a noun while abruptness is a noun.

Word	Noun	Adjective	Verb	Adverb
abrupt	No	Yes	No	No
abruptness	Yes	No	No	No

abrupt (noun)	abruptness (noun)
	the quality of happening with headlong haste or without warning
	the property possessed by a slope that is very steep
	an abrupt discourteous manner

abrupt (adjective)	abruptness (adjective)
surprisingly and unceremoniously brusque in manner
marked by sudden changes in subject and sharp transitions
dangerously steep
exceedingly sudden and unexpected