I. ˈded-lē adjective
( dead·li·er ; -est )
Date: before 12th century
1. : likely to cause or capable of producing death
deadly poison
2.
a. : aiming to kill or destroy : implacable
a deadly enemy
b. : highly effective
a deadly exposé
c. : unerring
a deadly marksman
d. : marked by determination or extreme seriousness
3.
a. : tending to deprive of force or vitality
a deadly habit
b. : suggestive of death especially in dullness or lack of animation
deadly bores
a deadly conversation
4. : very great : extreme
• dead·li·ness noun
Synonyms:
deadly , mortal , fatal , lethal mean causing or capable of causing death. deadly applies to an established or very likely cause of death
a deadly disease
mortal implies that death has occurred or is inevitable
a mortal wound
fatal stresses the inevitability of what has in fact resulted in death or destruction
fatal consequences
lethal applies to something that is bound to cause death or exists for the destruction of life
lethal gas
II. adverb
Date: before 12th century
1. archaic : in a manner to cause death : mortally
2. : suggesting death
3. : extremely
deadly serious