1. sufficient to cause death: "a lethal cocktail of drink and pills"
▪ very harmful or destructive: "the Krakatoa eruption was the most lethal on record"
▪ (in a sporting context) very accurate or skilful:"a lethal drop-shot"
Word Originlate 16th century (in the sense ‘causing spiritual death’): from Latin lethalis, from lethum, a variant (influenced by Greek lēthē ‘forgetfulness’), of letum ‘death’.