deadly vs lethal

deadly and lethal both are adjectives.

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

As adjectives, deadly and lethal are synonyms defined as:

deadly (adjective)	lethal (adjective)
exceedingly harmful	of an instrument of certain 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

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