lethal (adj.)

• baleful
• baneful
• brutal
• corrosive
• corrupting
• corruptive
• counterproductive
• damaging
• deadly
• deathly
• deleterious
• destructive
• detrimental
• disadvantageous
• distressing
• fatal
• feral
• harmful
• hurtful
• injurious
• internecine
• killing
• malefic
• malevolent
• malign
• malignant
• mischievous
• mortal
• noisome
• noxious
• ominous
• pernicious
• pestilent
• pestilential
• poisonous
• prejudicial
• savage
• toxic
• venomous
• vicious
• virulent