deadly

modif.

1. Causing death

   fatal, lethal, murderous, mortal, deathly, poisonous, toxic, homicidal, bloody, noxious, destructive, venomous, deleterious, baleful, malignant, terminal, virulent, injurious, pestilential, pestiferous, death-dealing, carcinogenic, suicidal, bloodthirsty, cannibalistic, life-threatening, killing, baneful, pernicious, harmful, violent, inevitable; see also dangerous 2, destructive 2.

   Antonyms healthful*, reviving, beneficial. *

2. Very tiresome

   boring, tedious, tiresome; see dull 4.

deadly is applied to a thing that can and probably (but not inevitably) will cause death a deadly poison; fatal implies the inevitability or actual occurrence of death or disaster a fatal disease, a fatal mistake; mortal implies that death has occurred or is about to occur and is applied to the immediate cause of death he has received a mortal blow; lethal is applied to that which in its nature or purpose is a cause of death a lethal weapon, a lethal dose