deadly vs deadliness

deadly is not a noun while deadliness is a noun.

Word	Noun	Adjective	Verb	Adverb
deadly	No	Yes	No	Yes
deadliness	Yes	No	No	No

deadly (noun)	deadliness (noun)
	the quality of being deadly

deadly (adjective)	deadliness (adjective)
exceedingly harmful
extremely poisonous or injurious; producing venom
involving loss of divine grace or spiritual death
(of a disease) having a rapid course and violent effect
causing or capable of causing death
of an instrument of certain death

deadly (adverb)	deadliness (adverb)
(used as intensives) excessively
as if dead