Deadly a. : Capable of causing death; mortal; fatal; destructive; certain or likely to cause death; as, a deadly blow or wound.

Deadly a. : Aiming or willing to destroy; implacable; desperately hostile; flagitious; as, deadly enemies.

Deadly a. : Subject to death; mortal.

Deadly adv. : In a manner resembling, or as if produced by, death.

Deadly adv. : In a manner to occasion death; mortally.

Deadly adv. : In an implacable manner; destructively.

Deadly adv. : Extremely.

Example:
How Deadly is the swine flu and what is the mortality rate from contracting it?

Taxonomy
death, Merriam-Webster Online Dictionary, dead, Dictionary, webster, Word Games, Webster Online Dictionary with audio pronunciations, cause of death, destruction, cause death, thesaurus, adjective, glossary, english, language, ESL, Search, ly.

Defination from the web:
deadly from the Merriam-Webster Online Dictionary with audio pronunciations, thesaurus, Word of the Day, and word games. ... 1 : likely to cause or capable of producing death <deadly poison> ...