deadly vs lifelessly

deadly is an adjective but lifelessly is not an adjective.

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

As adverbs, deadly and lifelessly are synonyms defined as:

deadly (adjective)	lifelessly (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)	lifelessly (adverb)
(used as intensives) excessively	as if dead
as if dead	without animation or vitality
	in a lifeless manner