lethal /ˈliː.θəl/adjective 1noun 3forms 3 adjective1 •strong or dangerous enough to kill someone noun3 •Any weapon that causes death. •An allele that causes the death of the organism that carries it. •One of the higher alcohols of the paraffine series obtained from spermaceti as a white crystalline solid. formslethals · more lethal · most lethal