lethal

Etymology 1

Learned borrowing from Latin lētālis (“deadly, mortal, fatal”), improperly written lēthālis, from lētum (“death”), improperly written as lēthum, from a supposed connection with Ancient Greek λήθη (lḗthē, “oblivion, forgetfulness”).

adj

1. Of, pertaining to, or causing death; deadly; mortal; fatal.
   Whether modern, industrial man is less or more warlike than his hunter-gatherer ancestors is impossible to determine. The machine gun is so much more lethal than the bow and arrow that comparisons are meaningless. 2013-07-20, “Old soldiers?”, in The Economist, volume 408, number 8845

noun

1. Any weapon that causes death.
2. (genetics) An allele that causes the death of the organism that carries it.

Etymology 2

Abbreviation of “lauric acid ethereal salt”, so called because it occurs in the ethereal salt of lauric acid.

noun

1. (chemistry) One of the higher alcohols of the paraffine series obtained from spermaceti as a white crystalline solid.