deadly vs deathly

deadly and deathly both are adjectives.

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

As adjectives, deadly and deathly are synonyms defined as:

Other synonyms of deadly include mortal.

deadly (adjective)	deathly (adjective)
exceedingly harmful	having the physical appearance of death
extremely poisonous or injurious; producing venom	causing or capable of causing death
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)	deathly (adverb)
(used as intensives) excessively	to a degree resembling death
as if dead	to an extreme degree