'[Middle English, fateful, from Old French, from Latin ftlis, from ftum, prophecy, doom; see fate.] Synonyms: fatal, deadly, mortal, lethal These adjectives apply to what causes or is likely to cause death. Fatal describes conditions, circumstances, or events that have caused or are destined to cause death or dire consequences: a fatal illness. Deadly means capable of killing: a deadly poison. Mortal describes a condition or action that produces death: a mortal wound. Lethal refers to a sure agent of death that may have been created solely for the purpose of killing: execution by lethal injection.