deadly Play adjectiveCausing or able to cause death.adverbIn a way resembling or suggesting death; as if dead. SYNONYMS banefuldangerousdeath-dealingdeathlydeleteriousdestructivedetrimentalfatalharmfulincurableinjuriouslethallife-threateningmalignantmephiticmortalnocuousnoxiousperniciouspoisonousterminaltoxicunhealthyuntreatable