deathly vs deadly

deathly and deadly both are adjectives.

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

As adjectives, deathly and deadly are synonyms defined as:

Other synonyms of deathly include mortal.

deathly (adjective)	deadly (adjective)
having the physical appearance of death	exceedingly harmful
causing or capable of causing death	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

deathly (adverb)	deadly (adverb)
to a degree resembling death	(used as intensives) excessively
to an extreme degree	as if dead