lethal//ˈliːθəl//B2Frequency Level 10NeutralAdjectivelethalCanonical formmore lethalComparativemost lethalSuperlative1Causing or capable of causing death.The snake's venom is lethal to humans.2Extremely harmful or destructive.The combination of heat and humidity can be lethal to crops.SynonymdeadlyfatalmortalAntonymharmlesssafe