1. superlative form of deadly; most likely to cause death or most fatal
Usage: superlative degree of 'deadly'
2. superlative form of deadly; most resembling or suggestive of death
Usage: figurative use; superlative degree

Examples

• The deathliest poison known to science is found in certain frogs.
• That was the deathliest attack the city had ever experienced.
• The deathliest diseases of the medieval period were plague and cholera.
• His deathliest enemy finally surrendered.
• The deathliest silence fell over the room after the announcement.
• Among all the weapons, this one proved deathliest in combat.