LETHALLY
Etymology
Adverb
lethally (comparative more lethally, superlative most lethally)
In a lethal manner, in manner which is or will be fatal.
Source: Wiktionary
LETHAL
Leth"al, n. Etym: [Lauric + ether + alcohol.] (Chem.)
Definition: One of the higher alcohols of the paraffine series obtained
from spermaceti as a white crystalline solid. It is so called because
it occurs in the ethereal salt of lauric acid.
Le"thal, a. Etym: [L. lethalis, letalis, fr. lethum, letum, death:
cf. F. léthal.]
Definition: Deadly; mortal; fatal. "The lethal blow." W. Richardson.
– Le"thal*ly, adv.
Source: Webster’s Unabridged Dictionary 1913 Edition