deadliness vs deadly

deadliness is a noun but deadly is not a noun.

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

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

deadliness (adjective)	deadly (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

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