lethal

/ˈlē-thəl/

Latin letalis, lethalis, from letum death

adjective

  1. of, relating to, or causing death

  2. capable of causing death

  3. gravely damaging or destructive : devastating

death by lethal injection

lethal chemicals

deadly mortal fatal lethal mean causing or capable of causing death. deadly applies to an established or very likely cause of death. mortal implies that death has occurred or is inevitable.

noun

  1. an abnormality of genetic origin causing the death of the organism possessing it

  2. lethal gene

noun

  1. a gene that in some (such as homozygous) conditions may prevent development or cause the death of an organism or its germ cells —called also lethal factor, lethal mutant, lethal mutation