What is the meaning of deadly?

adjective

• Causing or capable of causing death.
  • usage: "a fatal accident"; "a deadly enemy"; "mortal combat"; "a mortal illness"
  • synonyms: deathly, mortal
• Of an instrument of certain death.
  • usage: "deadly poisons"; "lethal weapon"; "a lethal injection"
  • synonyms: lethal
• Extremely poisonous or injurious; producing venom.
  • usage: "venomous snakes"; "a virulent insect bite"
  • synonyms: venomous, virulent
• Involving loss of divine grace or spiritual death.
  • usage: "the seven deadly sins"
  • synonyms: mortal
• Exceedingly harmful.
  • synonyms: baneful, pernicious, pestilent
• Of a disease. ( having a rapid course and violent effect)

adverb

• As if dead.
  • synonyms: lifelessly
• Used as intensives. ( extremely)
  • usage: "she was madly in love"; "deadly dull"; "deadly earnest"; "deucedly clever"; "insanely jealous"
  • synonyms: madly, insanely, deucedly, devilishly