LETHAL

I. adjective Etymology: Latin letalis, ~is, from letum death Date: circa 1604 1. of, relating to, or causing death , capable of causing death , gravely damaging or destructive ; devastating , very potent or effective , see: deadly ~ity noun ~ly adverb II. noun Date: 1917 an abnormality of genetic origin causing the death of the organism possessing it, ~ gene