WordWeb Online

1. Causing or capable of causing death
   "a deadly enemy"
   - deathly, mortal
    
2. Of an instrument of certain death
   "deadly poisons"
   - lethal
    
3. Extremely poisonous or injurious; producing venom
   "deadly snakes"
   - venomous, virulent
    
4. Involving loss of divine grace or spiritual death
   "the seven deadly sins"
   - mortal
    
5. Exceedingly harmful
   - baneful, pernicious, pestilent
    
6. (of a disease) having a rapid course and violent effect
    
7. So lacking in interest as to cause mental weariness
   - boring, deadening, dull, ho-hum, irksome, slow, tedious, tiresome, wearisome, unamusing, draggy

1. As if dead
   - lifelessly
    
2. (used to intensify) extremely
   "deadly dull"; "deadly earnest"
   - madly, insanely, deucedly, devilishly

Derived forms: deadliest, deadlier

See also: dead, deadliness, fatal, irremissible, noxious, toxic, uninteresting, unpardonable, virulent

Encyclopedia: Deadly