I. ˈlēthəl adjective
Etymology: Latin lethalis, letalis, from letum death + -alis -al; probably akin to Latin lenis soft, mild — more at let
1. archaic : of or leading to spiritual death
discoursing of sinners and their lethal end — Charles Reade
2.
a. : of, relating to, or causing death
the two convicted men will soon enter the lethal chamber — William Mayer
in mice the mean lethal dose was more than twice as large as the mean paralyzing dose — Science
the lethal fire that destroyed the building and all its occupants
b. : capable of causing death : deadly
wished I had a gun or some lethal weapon, that I might destroy him — Bram Stoker
prohibits the transportation in interstate … commerce of lethal munitions — U.S. Code
the increasing quantity of lethal carbon monoxide poured into the air by the internal-combustion motor — Lewis Mumford
gathering edible mushrooms … is a pleasant but potentially lethal pastime — Pfizer Spectrum
3. : causing damage or destruction : devastating
showed a lethal skill in his dissection of the … book — Times Literary Supplement
a lethal attack by the opposition caused him to resign
used the lethal veto ten times to block action in the security council — Time
Synonyms: see deadly
II. noun
( -s )
1. : a lethal substance
2.
a. : an abnormality of genetic origin causing the death of the organism possessing it usually before maturity
b. : lethal gene