deadly vs madly

deadly is an adjective but madly is not an adjective.

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

As adverbs, deadly and madly are synonyms defined as:

Other synonyms of deadly include deucedly, devilishly, insanely.

deadly (adjective)	madly (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)	madly (adverb)
(used as intensives) excessively	(used as intensives) excessively
as if dead	in an insane manner
	in an ungovernable manner